If ever there was evidence that game designers hate RPG fans, Demonic Spiders are it.
MapleStory has an enemy in one area called the Stirge. It is a goddamned-bat-like creature, which flies just above the hit area of most player's weapons. Combine this with a fairly high attack power, and the required quest that Dual Blades have to kill these things for, and you've got some serious Fake Difficulty.
Ever since the patch that revamped Victoria Island, Stirges have been well and truly relegated to mook status. In fact, most enemies hardly even pose a threat to players anymore due to power creep.
Okage: Shadow King was full of these. Foes generally either packed nasty status effects, could deal enough damage to kill you in a few hits, or had more HP than a freaking tank. Squads varied, and often had a combination of these, aided by legions of weaklings. This actually kept the game interesting though, as strategy was required for just about every encounter, but you could avoid fights to balance things out.
Final Fantasy Adventure had all sorts of enemies that could inflict status effects, but none were worse than Moogle. Upon being Moogled, you lose the ability to do anything but move, and your defense drops to 0. Defense is extremely important in this game; with 0 defense, you can be killed in a single hit if you never leveled up stamina. Enemies that can inflict Moogle must be engaged with an escape route in mind. Your best bet is moving between rooms until the effect wears off.
Any enemy in Secret of Mana that can summon more enemies, and slimes in particular. Fortunately, they are limited to having three monsters on the screen, but this is small comfort when the last one standing keeps making two clones before you have the chance to finish it off! Furthermore, the red slimes would set you on fire if you got too close while the blue slimes would turn you into a snowman!
Another annoying enemy type were Tomato Men and other enemies that could not be harmed by regular attacks (unless you got a critical hit). This forced you to either charge up your weapon (a slow and dangerous process when other mooks are beating on you), use magic (even though your mana pool is very limited early in the game), or run like a chicken. And yes, some types of slimes fell into this monster category.
Probably the worst offender was the Shape Shifter. It'd spawn a random enemy from a permanent set. One of the enemies it spawns? Eggplant Man. When you encounter a Shape Shifter for the first time, Eggplant Men is an enemy encountered at least two dungeons ahead. And to rub salt in the wound, Eggplant Men spawn Needlelions, which are guaranteed to kill a character at the point Shape Shifters are first encountered. And to rub lemon juice in that would, Shape Shifters are one of the hardest enemies to kill thanks to absurdly high defenses. You're better off running like hell.
Practically any enemy that can cast spells can become a huge bastard. Magic in this game is fundamentally broken; upon casting a spell, the caster becomes invulnerable until the spell finishes, and you will be hit no matter where you are on the screen. An enemy spamming spells cannot be hurt, but the spells will be hurting you.
Nearly any monster can become this, depending on circumstances, when night falls in Mana Khemia: Alchemists of Al-Revis. Ones that are already nasty can get boosted to the point where they become a Boss in Mook Clothing—without the usual rewards and fanfare the game attaches to such.
One in particular is the side job where you have to fight 3 Kyuubis in the Japanese PSP version; item lock, no HP/SP healing and fast initiative will ensure you will lose. HARD.
In Dragon Quest I, many monsters can put you to sleep before you can act, and you will be at the mercy of the RNG until (or IF) you wake up. The Magiwyvern has a tendency to bludgeon you to death in your sleep. The Starwyvern has deadly flame breath (which ignores your defense), high HP, high attack power, and Healmore (meaning it can heal faster than you can hurt it if it decides so). The Wizard possesses both Sleep and Hurtmore and is resistant to your magic. The Armored Knights in the endgame have both Healmore and Hurtmore, and Red Dragons combine the worst of everything, since they have both Sleep and Healmore, and do the worst melee and fire breath damage out of all mooks in the game.
Dragon Quest II has several, but the most infamous example has to be the Gold Batboons/Bat Demons in the final area of the game. Those babies could potentially wipe out your entire party in one turn with their Sacrifice spell. And unlike the Rockbombs/Bomb Crags of later games, they don't wait until you've damaged them to do it. They can do it at any given moment, even on their first action of the battle, if they feel like it. And they can act before your party, if the RNG says so. And this spell has a 100% success rate of working. Even a party at the maximum level can be insta-killed if the random number generator decides you don't deserve to live any more.
Dragon Quest III introduced the Man Eater Chests to the series (and later on in the same game, the upgraded mook, the Mimics). The lesser can inflict terrible blows, hits like a freight train and can make your allies fall asleep by emitting sweet breath. The Mimics, however, can kill your party members with Defeat. It can also make you fall asleep and it can also leech magic points from you to it. Moreover, the Mimic chests attacks twice in one turn. Have fun!
Dragon Quest V has the Evil Masters and Red/Blue Eaters. Eaters come in large groups and have high agility and ridiculously strong attacks. Evil Masters can summon a lot of these, and WORSE, if an Evil Master defends instead of attacking, another goddamn Evil Master shows up right then and there, and unlike most reinforcements, has an instant turn.
And Dragon Quest VII gives us another upgraded version of the Mimic line; The Pandora's Box. Which might as well be a Mimic with stronger levels and Drain Magic which surprise, leeches MP off it's target (AKA your party making it Weird dance with a different name [and maybe more potent]). Unlike it's namesake there is little hope to be had when facing this monster.
The Dead Ringers in Dragon Quest VIII can not only level themselves up repeatedly, but call in reinforcements...who can call in more reinforcements that call in even more until you're dealing with 8 of them, at which point they unleash an attack that can wipe out your entire party.(How appropriate that said attack is to chime out the Game Over music from DQ1.)
Fucking Boa Bishops from Dragon Quest IX. Way too much HP, way too fast (both in battle and out), always attack twice, have an automatic sleep spell, have a hit-everything-spell, often appear in twos and threes... Oh, and to add insult to injury, their snake tentacles take up so much space in the narrow grotto corridors where you find them that you can't sneak past them, and drags you into battle even when you're think you're out of its range.
In Tales of Phantasia's ice dungeon, there are enemies called "Ekim." One Ekim in a group of enemies is nothing to worry about. However, when they appear in pairs, they embody this trope. The first one will prevent you from reaching its partner, who will invariably cast the devastating spell Judgment. While your party recoils from the blow, both Ekim will begin to cast this spell and proceed to spam it until your helpless party is destroyed. To make things more irritating, it is possible to go for more than an hour without reaching a save point.
Speaking of Tales, in Tales of Innocence's secret dungeon, there is an enemy that resembles a bee. These generally come in groups, are incredibly fast, have great attack power and attack several times. By the way, the dungeon has 100 floors and you can only save by getting out of it.
The Svaltus is large humanoid thing about 10 feet tall and with a huge sword on its arm. It has a linear, long-range shockwave which can randomly stun you if it inflicts damage—which, given the attack power of the Svaltus, is pretty much every time it hits. Stun status renders you unable to move, heal, or in fact do anything but stand there and let it and its pals beat on you without fear of reprisal. They take reduced damage from bullet attacks and have a shield which they will use liberally and without restriction which eliminates bullet damage while active, making guns useless; And if you try to melee them, they will use a spin attack which will inflict the Zalure defence-down status effect on you and send you flying, unless you happen to block it. (don't count on that) Oh, and did I mention they like to spawn in packs?
Zamvapas and Galvapas are large quadrupedal creatures with an annoying tendency to charge, which they will do so for long distances. Against low-levelled players the charge does hefty damage, but even if you're level Awesome and evade every time, you still have to go chasing after them, at which point they will inevitably charge AGAIN, and AGAIN, and AGAIN. Repeat ad nauseam. In addition, they have obscenely high defence when hit anywhere but their head, making the risky head-on assault the only way for those without TECHNICs to do appreciable damage. Which inevitably leads to the irritating charge-chase-charge malarkey, over and over.
Grass Assassins are another instance of "large goddamned bats," unlike the Grass Assassins which appeared in Phantasy Star Online. They thoroughly enjoy charging, sending your character flying into the nearest wall every time it hits, even if you only take a single point of damage. They also possess a spit-take attack, which almost always inflicts the stun status effect should it do damage. Add to this the fact that Grass Assassins always seem to show up in packs, and will often take it in turns to use the spit-take, and the Grass Assassin is an exercise in controller-snapping frustration.
Ubakrada are another example from this game. All of their attacks, save their elemental projectile attack, comes with very little warning, and half have the ability to send a player flying should it cause any damage at all. These attacks include a charge, and a quick sweep that also serves to turn the creature about 90 degrees, making it almost impossible to get behind the thing, which is a useless tactic anyway, since it will just perform a back-kick and knock you down. And those elemental projectile attacks come in the ice and light varieties (depending on the element of the creature), which will freeze you solid or put you to sleep, respectively.
Phantasy Star Zero Arkzeins in the Arcaplant. These enemies will make your life a living hell. They don't look like much...But once they start attacking its hellish. They have a homing missile attack which in the higher difficulties will OHKO you if you're playing a squishy class like a newman or human force class(Human rangers might be on their last leg...). Their other attack is a quick machine gun volley which doesn't do as much damage but if you're whaling on it head on can whittle you're health down quick. Its last attack is a "rush" like skill where it tries to run you over sometimes scoring multiple hits making it sometimes even worse than the missile attack. If you're of the completionist fare, then have fun hunting down Arkzein Type Rs they're the same only turned up to 11 and are VERY rare. Luckily, these demonic spiders only appear in the Arca Plant and the Eternal Tower for the safety of your sanity. Unfortunately they often get spawn 2 at a time, and if you're really lucky they'll spawn 2 more. Seeing as you only get three revives unless you're playing in a party that hopefully didn't get mowed down thrice like you did these guys are a major pain in the butt.
In Wizardry 8 the general power of Standard Status Effects means that fighting almost anything that can inflict an ailment can turn into an exercise in frustration, especially if the monster is particularly fast. This tends to include Rynjin (insanity, turncoat), nightmares (fear, insanity, turncoat, blindness), most plants (blindness, sleep, poison), and undead (insanity, sleep, paralyzation, fear). Late in the game, enemy spellcasters like Rapax Templars can even use the same buffing spells as the party (with Missile Shield being far and away the most annoying, as it negates a large portion of ranged combat and causes one to waste precious ammo if one isn't careful).
And yes, the game does have bats. They're annoying because they're really fast, meaning unless you freeze, sleep, or drive the lot of them insane they will invariably surround your party. At low levels, this means taking a lot of damage. At high levels, they can even cause HP drain, which is harder to cure than death.
One of the nastier examples are the Pixies in the Trynnie trees. Their powerful magical debuffs can render most of your party impotent inside the first combat round, their fast reaction time means they'll almost always cast first, and there's something particularly humiliating about finding yourself constantly running away from roving gangs of tiny naked girls with wings.
On the other hand, that's really all they have. They also possess pitifully low HP, and if they cast anything but Blinding Flash or the like, a single application of an area-damage spell will typically kill them all in a single shot. Their higher-level cousins, such as Cliff Sprites, on the other hand, have the same attack spells and about five times as many hit points.
Wizardry VI: Bane of the Cosmic Forge and Wizardry VII: Crusaders of the Dark Savant had more than their share. What could make them truly nasty is that unless the player is very experienced at the game (and knows when what monsters start appearing, and in what numbers), the Demonic Spiders are indistinguishable from the normal mooks without a high mythology skill on one of the characters. Examples:
Qua'Tari look like Ban'Tari at first (and Ban'Tari aren't slouches), but it's when you realize that Blinding Flash isn't working, and that they're hitting HARD, that you realize these aren't your normal two-headed lions. Veterans know to beware when the kitties show up near Ukpyr.
Lizards in Wiz7 in general are one of the tougher enemy groups, but Komodo Dragons are truly dangerous. Resistant to most magic, lots of armor, hard-hitting, acid breath that hits multiple characters, and a chance to instant-kill characters with physical attacks...
Helazoids could also be frustrating at lower levels-fairly fast, resistant to magic, hit hard, and their laser cannons can hit back-rank characters. All but the weakest variety have a chance to instant-kill as well.
The tougher Rattkin qualify, too. Rattkin as a whole tend to be Glass Cannons, but the nastier ones really emphasize the "Cannon", adding in poison, instant death, and occasionally stoning as potential side-effects.
Savant Controllers and Kui Sa'Ka. Not very fast, but resistant to magic (noticing a trend?), good armor, lots of hit points, and the truly annoying psionic spells that like to make party members go insane.
And God help you if you run into Conqueladas...
The DS games in the Etrian Odyssey series generally start out dumping the player in an area where all enemies count as demonic spiders due to how weak the player starts out.
In the second stratum, you run into the flower-like Petaloids. They have an ability called Sleeper, which can (and often times, does) put your entire party to sleep, leaving you unable to act. They're bad in the second stratum, but near the end of the normal game, when you encounter 2 much stronger versions of them together with enemies that can two-shot most of your party, you begin to get very scared of them.
A clear example from the second game are Gigaboars, since it's the stopping point for many in the second stratum, forcing a serious training and reequipping stop. Gigaboars don't have much HP, all in all—180 is a pretty manageable amount for a party in that level. But they hit like mack trucks. As in, if you're using a Ronin or Dark Hunter in the frontlines? Oneshotted. And they have pretty decent speed too, so you can't use the most damaging attacks, since they're slow and you'll give them the first action that way.
Another star in the ending of the second Stratum of the second game is the Poseidon. A huge grass brachiosaur with about double the HP of almost everything else in the floor, which doesn't hit for all that much less than the areas F.O.E.s, and which has a move named Scurry that hits your whole party - yes, including the SquishyWizards in your back row - for huge damage. Additionally, it seems fond of blindsiding you (which poses the question of how in blazes you get blindsided by a goddamned Brachiosaurus), which means he gets a free turn to maul you into paste. And he almost never appears alone, to add insult to injury. Good luck avoiding them, since all resource-gathering points have a random chance of giving you a battle instead of an item, and Poseidons are a common opponent in these events.
The Great Lynx at the beginning of the third game. It appears in the first stratum if you stray too deep, and if you're a low level, it'll be faster and stronger than anything you have in your party, often downing characters with a single hit. In that same vein, the Largebill, which appears in the second floor of the first stratum during the day, and is the reason you'll be doing most of your exploration during the night early-game.
Venomflies in any of the games. They spit poison that's almost guaranteed to one-shot a party member by the end of the turn, and to make matters worse, in the second game they spit it at the entire party at once. And they are common!
From B-2F onward in the second Labyrinth in Legends of the Titan, we have the Hollows, who are nearly impossible to hit if you haven't bound their legs and hit very hard right back. Haven't been using bindings yet? Better start training that Sniper...
While the series' notorious F.O.E.s are generally regarded as an example of Boss in Mook Clothing, at least one can make a decent case for this trope. There's a type of bird FOE in the final stratum of the first game, known as "Macabre" in the original and "Depth Dancer" in the remake, and you will loathe them. They spawn randomly from the walls in a large room full of damage floors, barreling towards you at high speeds- and, making matters worse, in the original they will always back-attack you. They resist most types of damage, summon Goddamn Bats with an instant-death attack, deal heavy damage to the entire party with a blind effect, and there is a very high possibility of a second one catching you while you're still trying to kill the first one. Even at very high levels, your ability to survive areas infested with them is often entirely dependent on whether you can avoid them in the first place.
EarthBound and rest of the MOTHER series have a love affair with Demonic Spiders.
The Dali's Clock, which can attack you and freeze time in mid-hit, causing a long string of attacks.
Everything in the Department Store and Moonside is a Demonic Spider. The Enraged Fire Plug, the aforementioned Dali's Clock, and the infamous Scalding Coffee Cup are the worst, but the Mystical Record and the Musica aren't fun either.
The Demonic Petunia in Deep Darkness. Its only attack (a "giant blast of water" that is actually a PSI Fire Gamma spell) will hit all your party members for a ton of damage (unless you're protected against it).
There's also the Atomic Power Robot. It can freely use the "replenish a fuel supply" action (which heals whatever it's used on fully), and it explodes upon defeat. Not to mention it shows up in the area where you can get the Sword of Kings. If you want it, you will almost definitely be fighting a lot of battles, which means a lot of chances for these guys to join said battles and screw you over. You can, however, use the Mirror ability on them, letting Poo refuel your own party to full health. Don't think about how that works.
The Ghost of Starman. They cast PSI Starstorm Alpha at the start of every fight, which can kill three members of your party at once if you don't go first and get a PSI Shield erected. In the Very Definitely Final Dungeon they travel with the Final Starman, which is a Boss in Mook Clothing, and the Nuclear Power Robot (a tougher version of the Atomic Power Robot). If you don't kill them fast enough (and you might not, considering the Robot's healing abilities), they'll do a countdown and cast PK Starstorm Omega.
Then there are the Loaded Dice. They show up in an area where you only have one controllable character. Their only action is to call for help, which if successful will summon another enemy into the battle. These include Uncontrollable Spheres, which explode when defeated, and Care Free Bombs, which do nothing but throw Bombs and the occasional Super Bomb.
Mobile Sprouts aren't too hard to kill, but then they plant seeds and grow several more Mobile Sprouts, which plant even more seeds, which causes the situation to rapidly escalate beyond your control. Unless you have enough PP to hit them with PSI Rockin' Alpha, you could be in trouble.
Due to a notorious lack of product testing, MOTHER 1 has too damn many of these, especially in the last area of Mount Itoi. The one that immediately jumps to the forefront is Juana: it can deal 150 HP of damage with every regular attack if you're not using a shield, and it also comes with PK Thunder Gamma, PK Fire Beta, and PK Fire Gamma, which hit all party members. It uses PK Beam Gamma, which kills anyone not wearing a Franklin Badge. To top that all off, it can raise its defense to impervious levels with its "darling smile." It's bad enough alone, but it occasionally shows up with a Super Energy Robot (called SuperEnergy due to character constraints on the NES), which can heal an enemy completely. Your best bet is to run away when you see one unless you're traveling with EVE.
There's also Gargoyles, which hit for over 100 damage and cast PK Fire Gamma (hits your entire party for upwards of 90 damage), Oh Mooks (which can paralyze, blind and confuse party members) and Titanees, which have massive amounts of defense and turn party members to stone. And they attack you Every. Three. Steps.
MOTHER 3 has Trees, which take the worst qualities of the Woodohs from MOTHER and the Territorial Oaks from Earthbound. Not only do they explode, but they can summon MORE of themselves, and at the point in the game where you encounter them, you can very easily die from the flames if you aren't quick and are low on health.
Almost everything in the Volcano level is some form of this. The Mrs. Lavas will hit you with PK Fire Gamma for around 100 damage per party member, the Pyreflies are weak but fast and good at whittling your health down, and the Magmen have a tremendously powerful 'eruption' attack and can spawn Pyreflies. There's a reason they sell Flame Pendants in Saturn Valley.
Although, there is a very handy spot in the volcano that lets you abuse the respawning-magic butterfly trick, turning it into a Peninsula of Power Leveling.
The stationary Grated Yammonsters, which appear in the Sunshine Forest starting Chapter 4, have 387 HP (far more than the Slitherhens or Really Flying Mice), but the real danger of facing them is that they cast PK Freeze Beta, which can deal 30 or 60 more HP of damage than Lucas or Boney have HP, if they enter the Sunshine Forest before visiting the Railway (read: at around level 10). Worse, they guard presents, so you may accidentally run into them while trying to open one, and get a party member wiped while attempting to escape. Take caution while exploring Sunshine Forest early in Chapter 4.
Any Taboo Noise. They're stronger than the Noise they're based off of (except perhaps the drakes), have ridiculous amounts of damage reduction unless you have the light puck, requiring you to really move the puck efficiently if you want to hurt them at all, and actively seek you out during a scan. On top of all that is the fact that running away is disabled during Taboo fights, meaning that you can't even run from them.
Minks: the non-Taboo form of this enemy chain is actually deadlier than its Taboo form. Why? It can use a breath weapon that deals absolutely horrifying damage (the Taboo version doesn't). If it uses it on the top screen, it is virtually an instant kill-it is continuous, essentially impossible to block in its entirety, and can't be avoided on the two-dimensional battlefield of the top screen (unless the player's partner is Joshua and can levitate). The player's only real chance is to go hyper-aggressive and hope to kill it before it does the breath attack.
The Taboo Drake is annoying as hell to kill, too—especially if you've been dropping your level for the Ultimate drops. Top screen faces spears from above, bottom gets the standard Taboo treatment. It isn't as hard to kill in the New Game+ because you can use Joshua, who levitates, thus avoiding most of the drake's attacks.
Baldur's Gate II, and many other games based on Dungeons & Dragons, have mind flayers. You really don't want to mess with mind flayers if you have any other choice, as they will cause your party members to start attacking each other—and the ability that causes this is psionic, not magical, so it's really hard to defend against. Liches and dragons are also extremely dangerous, but they tend to be bosses. Note that while you can make yourself immune to their stun/hold/confusion attacks, there is no way to protect yourself from the INT-drain. The closest you have are temporary INT buffing potions. So even if you do get those spells, you still die if you are hit three times. (or less, if you are particularly low of intelligence).
One flayer-killing tactic is to raise undead to block them from getting ot you. Another, more effective tactic is to note where the passageways are and fill them up with traps, then choose someone expendable to open the door at the end.
Mordenkainen's Sword works wonders against Mind Flayers, as the swords are immune to the INT-drain.
Casting three simple spells on your characters would protect them from 99% of a mind flayer's arsenal, leaving them as slightly squishy monsters for your characters to plow through. Beholders, on the other hand, are extremely dangerous... until you get the Shield of Balduran, which deflects beholder rays back to their source. At which point beholders just become a source of amusement, as you watch them swarm your shield-equipped character and wipe themselves out. The players who don't get the Shield of Balduran, though, are in for a rough fight. Magic is a useful defense against mind flayers, but beholders can dispel the defenses you put up against them in one attack and then kill you the next. Their most deadly attack is a ray that serves as a Flesh to Stone spell. Not only will this end the game if it hits your main character, it will remove any effected character from your party. This isn't a huge deal from a gameplay perspective, as removed characters can just be recruited again when restored. From a roleplaying one, though, it's traumatic; removing a character from your party will instantly end your romance with him or her. You heard me right. Beholders can KILL LOVE.
For those who don't have the shield, the easiest way to take down Beholders is to use summoned monsters. Thanks to a quirk in the AI, Beholders don't use their rays on summons and try to bite them instead. While the Beholder is distracted by the summon, your party can hack it to death with minimal fuss.
An earlier example would probably be Umber Hulks. They're tough and cast Confusion with unnerving frequency at levels where you might not have the ability to dispel it or the items to protect against it. Once you get Death Spell though they die instantly. By the way, guess which monster type Mind Flayers are usually accompanied by? That's right, lots and lots of Umber Hulks.
It should probably be mentioned that BG2 scales certain encounters (mostly random ones) according to EXP. The Shadow Dungeon, if done at a high enough level, can contain liches in regular spawns. Spawns which also includes Bone Golems and Vampires.
If you don't have powerful enough magic weapons, we'd strongly advise against wandering the streets of Amn at night, because you will meet a vampire, and it will kill you. Their level drain and Dominate effects are also hugely annoying.
In the first game Kobolds. The Commandos anyway. Thanks to their habit of showing up in significant numbers, blocking chokepoints, bringing along plenty of other Kobolds as meatshields, and packing fire arrows which are absolutely deadly in a low level campaign like this one. They also show up early enough that you probably won't have anyone who can use spells like Fireball and Cloudkill. If your main character is a Squishy Wizard or Glass Cannon thief w/o adequate missile protection and/or fire resistance and the Commandos spot him/her, it's pretty much game over. Even worse, there's a thankfully optional dungeon where Kobold Commandos endlessly respawn — and it's mostly tight corridors that favor them and are bad news for a melee oriented party. Did I mention they also give paltry experience when slain? In the sequel they aren't as bad since they don't show up as often and your characters are beefier.
Another one from the first game: If you ever got caught stealing or had low enough reputation that they'd attack automatically, the Flaming Fist Enforcers would ruin your day.
Most of the different types of golems in the 2nd game can be defeated with minimal fuss. Stone golems are pushovers. Clay golems are even easier as long as you don't forget blunt weaponry (they resist everything else). Iron golems are bit beefier and have a nasty poison attack, but they are still managable. The Adamantite golems that show up when your party is higher level are another matter. These beasts don't rely on any special tricks — they are just huge powerful bruisers that resist damn near everything and can't even be scratched by anything weaker than +3 weapons. All you can do is buff up your melee characters and pray to the random number god. Adamantite golems are usually accompanied by other golems too.
Enemy mages are also fairly nasty to face, especially if they have friends. A single Confusion can cause your entire group to self-destruct as the frontline fighters arbitrarily decide they'd like to massacre the missile support rather than fight their actual enemies, meaning you get torn limb from limb by the mages' friends. And they usually turn up with a Contingencied Protection from Anything Short Of An Angry God combo, meaning that as soon as a fight breaks out they become almost impossible to hurt. Entire fights can boil down to whether or not Jaheira has Insect Plague.
In the first game, Sirines cast dire charm on your party and shoot you with poison arrows. Oh and they always come in groups.
In the first game, Giant Spiders also become this if you're out of antidotes. Due to the extreme damage done by poison in the first game (2 damage per second for over a minute of duration = 120+ damaqe, more than any character in the game can survive), a spider battle means that basically anyone hit by one is on a Time-Delayed Death timer you can't stop. They also No Sell the best low-level crowd control spell in the game (Web). Spiders are extremely common, and can be found practically everywhere.
Neverwinter Nights, another DnD game, has a bodak in the Jhaereg castle. This bastard has a gaze attack that kills instantly if you fail a Fort save. Did we mention that wizards, sorcerers, and rogues all have crappy Fort saves?
Not to mention an earlier and literal instance of the trope, the bloated dire spider. This thing is level 10, whereas most players will be level 7 at the most when they encounter it, and not only can it knock you down, rendering you defenseless for a painfully long amount of time, it has slow-acting strength draining venom, meaning unless you can cure yourself somehow, your damage output will slowly be reduced to nothing and you'll become so encumbered you won't even be able to walk at a normal speed.
The expansions give us the secret room in the final dungeon of the interlude of Shadows of Undrentide that contains eight Basilisks (eight save-or-die effects per round...), the Bonus Dungeon under the Beholder lair in Hordes of the Underdark (all magic items are rendered nonmagical for most of that dungeon (which nerfs non-casters) and magic does not function (which nerfs spellcasters), and while its occupants' aren't much of a threat normally once you've lost all magic their Strength-drain effects begin to add up), and the Beholders themselves (with infinite-use petrification effects, no less).
Another vanilla NWN example: high-level duergar in the fire giant dungeon. If you had enough experience, groups of deep dwarves would frequently turn up with a mage rocking Phantasmal Killer, a spell which instantly obliterates you if you fail both a will and a fort save, and still hurts if you pass the fort.
In both games, thri-kreen (mantis warriors). They're incredibly fast, tough, and have a paralysing bite that makes it pretty sure one of your meat shields will be incapacitated before having even a chance to strike. So much that fighting them one-by-one is actually a less favorable option than facing a swarm of them — then at least you can spam offensive spells more efficiently.
Star Ocean: Till the End of Time has a few. Proclaimers are angelic monsters that perform a similar function in our universe as agents do in The Matrix use, every few seconds, a high damage attack that is unblockable and has a longer range than Maria's pistol in all directions, not to mention being encountered throughout the game starting about halfway until the predictable controller/screen interfacing inevitably ensues. Wisps have an even stronger all round attack , and to make matters worse there's a room in the Bonus Dungeon where the player must defeat ten groups of them followed by a (thankfully easy) boss without saving. Decahedrons and crystal statues are so fast that landing more than one blow is nearly impossible, never flinch and, needless to say, have lethal attacks. Most guides also mention Convictors (proclaimers' big brothers) in this context.
Much, much worse are the Sooties in the bonus dungeon, Sphere 211. Not only do they hit for insane amounts of damage and are much, much faster than you... they're about six inches high (meaning many attacks simply can't hit them) and are essentially mobile dust clouds with cute little caps and glasses on. Not just frustrating, but embarrassing at the same time.
Did you all forget the part of Sphere 211 you're supposed to go through during the story? The soldiers there are just a minor nuisance, but all the robots? They rip you to shreds. Especially the spider-like ones with the missile spam that juggles you in midair, which happens to be a strong attack so it breaks your AAA, and their AAA happens to be the first one in the game to heal the user, meaning if you screw up a weak attack they're getting healed. Oh, and while one by itself can be manageable, they often come in twos so that they can take turns juggling you. Have fun
Star Ocean: The Second Story has Salamanders and their palette swaps, which have a breath attack that, in theory, hits the character(s) in its path 2-3 times and pushes them away. However, very often, obstacles or the arena boundary prevent the characters from being pushed, and the attack hits over a dozen times for an instant kill. As if that weren't enough, it can cause some of the worst Standard Status Effects depending on which palette swap it is.
In the Shin Megami Tensei series, any enemy can be a Demonic Spider if they have an attack that any of your characters are weak to— doubly so in Nocturne, IV, Digital Devil Saga, and Persona 3 or 4, which use the "Press Turn" and "One More" systems respectively that allows for more turns by exploiting weaknesses. This works for and against you. Funnily enough, there aren't any actual demonic spiders.
In almost any game in the series, Rangda. She's pretty much the only random encounter that reflects physical attacks and only has one elemental weakness.
All four enemies found the in the Second Kalpa's cursed hallway. Tao Tie has a cheap insta-kill that almost never misses. Abaddon has a ton of HP and is heavily resistant to all types of magic. Nyx has powerful Ice spells as well as a cheap combo of moves that puts your party to sleep, and then kills everybody that's asleep. Flauros can drastically reduce your attack and then smack you around with moves like Deathbound and Iron Claw, both of which hurt like hell. Yeah, good luck fighting these assholes, especially with your HP continually draining.
Persona 3, already a difficult game, had the difficulty ramped up to 12 in the re-release, Persona 3: FES. FES added a Hard Mode to the original game, which turns every single monster in the game into a Demonic Spider, and every boss into That One Boss. Amongst the changes—Your chance to run is lowered to single digits; enemies spells do over double damage; Enemy instant kill spells are MUCH more effective; and the Persona Compendium, which in Normal mode allows you to recreate past Personae for a pittance, has it's prices upped by 400 PERCENT. The difficulty isn't insurmountable, but does require very careful, intelligent play, and many, many savegames. FES even adds an expansion that ups the difficulty even further, removing your ability to resummon past Personae. There's one bright spot though; if you sneak up on a Shadow, your surprise round grants you auto-success on escaping in case you run across something that would destroy you several times over. It's small comfort, but there you go.
A more specific example: the Void Giants in Monad. Physical attacks heal them. Extremely high magic defense. Repel Light and Dark (as in, they bounce them back to you.) Armed with the highest-level of aforementioned Light and Dark spells (single-target and group versions!) as well as Myriad Arrows and Deathbound, which are very high-level multi-hit, all-party Pierce and Slash attacks, respectively. And they come in groups of two at least. Even if you sneak up on them, if you see two (or more) get consecutive turns then you might as well reset the game (or fuse a Persona that Nulls/Repels/Absorbs Pierce, Slash, Light, and Dark, and just say goodbye to the rest of the party.)
Before them, you get to do battle with the Creation Relics on floors 65-88. Their only weakness is Darkness—but all this means is Mudo is marginally more effective, and by this point you probably gave up on it working and don't have it on any Personae. They know Magarula, which they love to use in a row; two in a row will kill most of your party. And to top it off, if you can't kill them down to one in a single round (and they do love to come in threes), they know Diarama, which will undo all your hard work. Oh, and they can self-destruct when on low HP. Bonus points: they're the Subjugation Request for that level—you have to hunt them down. The really weird part is that otherwise, 65-88 is one of the easiest stretches of Tartarus, and the Relic enemies in the next block are downright pathetic by comparison. They reappear in part 2 of Malebolge, the first level of The Answer. And they're every bit as annoying, if not more so. The Relics now have more HP, know Twin Shot (a powerful Strike attack that hits twice), and on top of their original resistances, they now bounce back Strike and block fire attacks.
Any Jotun-type enemy is bound to become this. Each of them are resilient enough to qualify for Boss in Mook Clothing status, even if you exploit their weaknesses, and they hit REALLY hard. Appropriately enough, when you finally encounter one as a boss, it absorbs everything but Pierce attacks.
Many of the Crimson Shadows, both in The Journey and The Answer. The Avenger Knight in The Answer is one such example. He shows up in Cocytus - the second dungeon in the game - and can very easily rip you a new one if you're caught off-guard, and/or thought he would be easy like he was in The Journey or Persona 4, in which case you'd be dead wrong. He has no weakness you can exploit, quadruple-digit HP, blocks both types of instant-death spells, reflects Pierce (Aegis' attack type), and has the very nasty combination of Elec Break (to nullify a character's resistance to electric attacks) and Mazionga (second-tier electric spell that hits the whole party).
The Berserk Turrets, also in The Answer, are truly vicious. You know it's going to be bad when Fuuka pleads you to run away from them. They always show up in groups of five, have really high defense against everything, including their weakness (electricity), and they don't die from a single All-Out Attack. And once their turns start rolling around, the Turrets fall into a pattern; hit someone with Agidyne, then sweep the party with Heat Wave. The only spot of hope there is shows up when the A.I. Roulette spins in your favor and the Turrets waste their turns hitting someone that's immune to fire. And they're Crimson, which means they're rare.
Remember the World Balance? You know, that boss from Persona 3 that knows every -dyne spell and responds to Magic Mirrors with Megidolaon? Yes, it shows up as a random encounter in The Answer, with all its moves as a boss and quadruple-digit HP. And it isn't even Crimson, which means it's more common than not!
The Grudge Towers, in The Answer, have over 1000 HP, high defenses, Megidolaon, and come in groups of four. Woe be to you should they decide to hit you with four party-wide unresistable Megidolaons in a row. Thankfully, they're a crimson shadow, so they're relatively easy to avoid.
Persona 4 has the Wondrous Magus. It shows up fairly often at the higher levels of the bathhouse dungeon and likes to spam Zionga, Mazio and Maragi which at least two members of your party are weak against. It also doesn't have any weaknesses, take a while to kill, rarely shows up in parties of less than three and you can't even switch out for party members that are stronger against them until later.
From the same game, Marukyu Striptease has a random encounter that is a lot more common than it should be; four Idle Basalts and a Persistent Fuzz. The Fuzz can and will bounce back any spell used on it, leaving you with physical attacks to take it down. And even though it has no spells of its own, its physical attack does tremendous damage. And the Basalts have no spells either, but their attacks do even more damage than the Fuzz's. They're weak to ice, but good luck keeping them down with it. If you try physical attacks on it, you'll find that they resist it 20-fold. Fortunately, these two only show up on two floors of the dungeon.
Any random encounter with the word "Basalt" in its name is going to be a Demonic Spider. They greatly resist (and later outright ignore) physical attacks, have unpredictable weaknesses, and while they don't have many skills, their regular attack hits like a ton of rocks. Oh, and one type of Basalt— the Selfish Basalt— resists Almighty. You will, more often than not, drain half your collective SP getting everyone's health back up after fighting a group of Basalts— assuming, of course, you survive the encounter in the first place.
Persona Q has the Burning Beetle, which appears in the third floor of the first labrynth, and exists to tell you the game has stopped screwing around. It can attack twice per turn, hits really hard, has a ton of HP and can use full-party hitting Fire spells and inflict Magic Bind. It's also resistant to both One-Hit Kill elements, so you can't cheap your way out of it. It also tends to be the thing to ambush you on Power Spots on this floor.
Around the end of the second floor, you have Justice Swords, which use Toxic Slice and Stun Slice, attacks that have a very high chance of causing Poison or Paralysis. They wouldn't be so bad if they didn't have a tendancy to show up in groups. In particular, there's one event that tricks you into thinking you'll get a free item... but instead pits you against five of these at once.
The Heat Balance, also from late into the first dungeon, is incredibly tough for the point you fight it at, because it happens to know Mind Charge (nearly triples the power of the next spell used, a move that's a Game Breaker when used by you and often only found on very late game Personas). Combined with the fact they have full party-hitting spells...
Possessive Cupids. These appear in the second labrynth, and are incredibly fast. They love to spam Thorn Chains, which not only does a lot of damage, but has a good chance of binding the target's magic, too. They can be one-shotted with a Mudo spell, but if they bind your Mudo user's magic they can rack up damage very fast. They also tend to appear in pairs.
The third labyrinth features Phantom Mages(wind), Rainy Pots(Electricity),Phantom Masters(Fire), and Ameniti Ravens(Ice), who all share a simple yet deadly tactic. They first cast an -Element- Corrosion Spell to make your entire party weak to their preferred element. Then they cast Magarula/Mazionga/Maragion/Mabufula to massacre the party. If you can't remove the debuffs or kill them quickly, you could find yourself staring at the game over screen very quickly, especially if they ambushed you.
Shin Megami Tensei: Strange Journey does away with extra turns—instead, exploiting enemy weaknesses will cause same-alignment demons (and you, if you're of the same alignment) to perform a "Demon Co-Op" attack for extra damage. Thankfully, enemies CANNOT do this. However, you still need to be on the lookout for enemies with spells that have "Mudo" in the name, as well as enemies with stoning attacks (an instant Game Overif it hits you) or attacks that cause the dreaded "Bomb" status, which turns a party member into a bomb that explodes on hit.
King Frost will, if not killed quickly, heal himself back to full health over and over again and spam Mabufudyne and Explosive Fist between heals. And if he's with other mooks when he casts his healing spell, those mooks are also completely healed. Makes sense that he shows up in Eridanus.
Pisaca just loves to cast the Bomb status on your party, and unless you have Dis-Bombs, they will deal tremendous damage to your party hitting whoever they bombed. Pray that it wasn't the main character.
Encountering Takeminakata when you first get the Enemy Search is a classic newbie trap. He has a good amount of HP for when you fight him, and high defenses to match. Additionally, he knows Zan-Ei, which is really strong and more or less becomes a One-Hit Kill if he's encountered under a new moon. To add insult to injury, he doesn't give out experience when you beat him; he does, however, give you a Forma that can be pawned off for 3,000 Macca.
Even for the level you encounter it in, Tao Tie is a pain. It nulls Physical and Gun attacksnote which makes any level grinding strategy that focuses on you going solo with a gun that inflicts Stone completely impossible and makes your character pretty useless in general, has over four hundred health, a skill that can inflict Fear on random enemies and a skill that inflicts Bomb on them. If you ever encounter a group of them and you don't have your best demons out your best bet is just to leg it.
The cake of Strange Journey's Demonic Spiders is taken by Futotama. It is a dozen levels ahead of the other enemies in the zones you can find it in, has no weaknesses, is immune to istant death, hits(hard) all of your party at once with normal attacks, has the ever-annoying Macca Beam and Strange Beam magic that will rob you of money and MP, can use Turn Tables to reverse any debuff you inflict it, and once you whittle its health down enough it will heal itself fully with Diarama.Luckily, it only appears if you use the Demon Search function, but if you factor in that you can't recognize it until you beat one...
The SFC version of Star Ocean featured enemies in the final dungeon that could turn you to petrify by contact. In a game where there's no guaranteed way to guard against petrification and if everyone's petrified, it's game over. They went the extra mile by designing random battles where your party starts out sandwiched between two of these enemies, guaranteeing that at least two of your party members are going to be petrified right at the start of battle.
The Fallout series has at least one enemy in each game that is guaranteed to lay a smackdown on your post-apocalypse scavenger ass. Deathclaws are the most well known of these radioactive abominations: in 1 and 2, they were merely superhumanly fast, brutish, and damaging. In 3, though, they gain some fantastically cheap moves, including the ability to leap from normal maximum effective shotgun range to into melee within a split second, while taking more punishment than a Super Mutant to kill. They can also take out a character with full health and the best non-power armor in a couple of swings. Best of all, they can be encountered in packs. The reason for this is cheap, though. The Deathclaw's attacks bypass DR and deal full damage to the player every time. However, if you can kill a Deathclaw, you can make a melee weapon which does the exact same thing— by mounting its claw to a glove on your hand. Sneak attacks and the Dart Gun— a weak weapon that cripples targets' legs so they go slower and can't perform "leaping" type attacks— are very useful for taking them out. With Better Criticals, you can kill one in 2-4 shots from Lincoln's Repeater, fewer if you use more powerful things like Fat Man or the like.
Fortunately, if you can cripple the Deathclaw's leg, it can be easy enough to, literally, keep out of arm's reach, as long as there isn't more than one coming at you, all you need to do against a crippled Deathclaw is keep your distance while shooting, and hope you don't have your back to a wall...
In Fallout 3, what you really need to watch out for are the Albino Radscorpions and Super Mutant Overlords of the Broken Steel expansion. The Albino Radscorpions are 1.5 times as large as the 2nd largest Radscorpions, have as much health as a Super Mutant Behemoth, and are random encounters in groups of 1-3. Overlords spawn anywhere with Super Mutants, carry Laser Shotguns which punch straight through power armour due to a hax effect that does unblockable 40 HP damage when used on the player. The shotgun fires 3 beams. Either that, or it comes with a Gatling Laser or a Super Sledge. Its health is a touch less than a Behemoth, but has higher endurance, and unlike the finite Behemoths, Overlords respawn. If you have the Chinese Stealth Armor and Silent Running perk, the easiest way to get rid of Overlords is to sneak behind them and drop a grenade or mine in their pants (by reverse-pickpocketing them to their inventory). This should kill them without fail.
Feral Ghoul Reavers from the same game share none of the weaknesses of the Overlords and Deathclaws and share the "may spawn whenever enemies of the same type may spawn". Dart guns only prevent their leap attack and cut their terrifying movement speed to 75% while not stopping them from hitting you VERY hard. They have insane perception that they will see you without fail even with 100 sneak, silent running perk, and Chinese Stealth Armor, making sneak attacks on them nigh impossible; they lack any weapons to shoot off, manage to have a deadl-accurate ranged AOE attack other Feral Ghouls lack, and share the 1200+ HP and 10 Endurance that Overlords have. For icing on the cake, Reavers can get bugged in mid-fight, turning them invincible for some time.
Of the three, only the Super Mutant Overlords give any loot worthy of the ammo expended to kill them. The other 2 give a few hundred bottlecaps at most
On a lesser scale, BS also has the Hellfire Troopers, who have advanced fire-resistant power armor and wield the deadly Heavy Incinerator, a very accurate long-range fireball thrower.
The PittExpansion Pack features Trogs as a replacement for Super Mutants. In practice, they more closely resemble weaker Deathclaws. Unfortunately for the player, they tend to come in packs of eight or more at times, and a higher-level player will encounter Trog Savages, which are every bit as strong as actual Deathclaws. To add further injury to injury, you can't bring in your Powered Armor or Frickin' Laser Beams, so higher-level players are going to end up with a much tougher time.
Shielded aliens in Mothership Zeta, especially the ones with Disintegrators, can become demonic spiders at higher levels, as their damage resistance and numbers increase as you level up.
Fallout Tactics has one special encounter with a huge pack of Deathclaws that takes place in complete darkness. Also, burst weapons in the series are famously unreliable against anything with decent armour. Quite a few of the robots in the same game are nearly invincible against anything except Energy Weapons, but the Behemoth Droid is perhaps the worst, given how well it is armed.
In Fallout 2, we have the Bounty Hunters. They are probably as bad as Deathclaws, or worse. Why? Because if your character is a child killer or just too damn evil, these guys attack you. Until the end game, they ALWAYS outgun you, using weapons you are only going to see somewhere further in the game. They also always outnumber you. This only gets worse as the game advances, and every one you kill drops your karma further, so even more powerful (relative to your level) mercs come after you next time if you happen to be on one of the karma "borders" the game seems to use for these encounters.
The Wanamingos in Fallout 2 are quite deadly foes, and you're likely to encounter them at a fairly low level as they're inside a mine in one of the early cities, and one of the quests demands that you go down there. And then you may be unfortunate enough to take the wrong entrance to the Redding mine, and encounter the "boss" wanamingo first. It doesn't help that it's hard to figure out what parts of their anatomy are comparable to those of humanoids. Not to mention that some weapons which are otherwise quite useful at this stage in the game are about as much use as a chocolate teapot against Wanamingos. In the Redding mines with an assault rifle? Time to find an earlier savegame.
The expansion pack Point Lookout adds in Swampfolk and Tribals. Despite wielding old-timey double barrelled shotguns or axes, and wearing overalls or robes, they are tougher than Enclave goons wielding plasma rifles and wearing high-tech powered armor (due to object effects on their weapons that pierce armor), and are about as common as regular raiders in the swamp. Oh, and there's reavers in the swamp. The next and final expansion, Mothership Zeta adds space aliens, whom, to be honest, are better than the frickin' hillbillies with their axes.
Fallout: New Vegas has Cazadores, giant mutant wasps that despite their flimsiness, attack insanely fast and usually come in large packs. And their poison attack can quickly kill the more unaware player (or those without Antivenom). For added Nightmare Fuel, the loud sound that a Cazador makes upon stinging a target is bugged, such that it plays at full volume regardless of how far away it is (as long as it is actually being rendered by the game), and regardless of who its target is. Thankfully, due to the small DT stat they have, a 10mm SMG with hollow-point (standard or jacketed HP) will tear them to pieces. Or you could shoot their wings out. Of course, this only really works if they're in front of you. The little bastards have a habit of being everywhere. And the larger Cazadors need more than just a shot in the wings to kill: first you have to cripple their wings, then cripple their legs, and then FINALLY put enough rounds into their skull to kill them. They get upgraded in Old World Blues.
Trying to get the Ratslayer at a low level? Have fun finding out Giant Rats are not easy pickings like they are in most RPGs. Here, they're fast, tenacious, and can chew through Metal and Combat Armor with ease.
If you're at a high level, you better not piss off any of the major factions. You'll get hit squads after you wearing Power Armor (NCR) or Centurion Armor (Legion) and armed with chainsaws, thermic lances, 12.7 mm SMGs, and anti-materiel rifles.
And the radscorpions are still around, of course. Giant radscorpions, in particular. You know it's bad when you're faced with an oversized arachnid and breaking out the ap ammo is a sound survival strategy, rather than an exercise in hilarious overkill. The locations where these guys are mixed in with their fast, sneaky barkscorpion cousins are especially... interesting.
And, if you think Giant Radscorpions are tough, Old World Blues gives us Robo Scorpions. These things are even tougher, can shoot laser from their tails, and if you think you had it, it will blow up after you finally defeat it.
The New Vegas DLC "Dead Money" introduced the ghost people. They're usually not the most damaging enemies, but their weapons are often designed to cripple limbs which will make you waste a stimpack in normal mode and a doctor's bag in hard mode. They also come back to life if their health is depleted and one of their limbs is not severed, so if you kill one with a gun and can't sprint up to the body fast enough to cut its limbs off, then you need to waste precious bullets to blow its limbs of from range. They wouldn't be nearly as bad if they weren't found (only) at the Sierra Madre, where all your stuff gets taken and the air may slowly kill you depending on difficulty. Here wasted supplies can mean death no matter what level you are at. They are also almost everywhere in the villa
The Mantises from the main game are mere Goddamned Bats, but the Zion Mantises from Honest Hearts hit almost as hard as entry-level Deathclaws.
In Fallout 2, the Enclave patrol random encounters. Seriously, just load your quicksave.
The half-coyote half-rattlesnake Nightstalkers. They inject poison (albeit less potent than cazadors), deal sizable melee damage, possibly bypassing Damage Threshold, and attack in packs. Worse, Lily's first quest has you fighting invisible Nightstalkers. Like most DLC creatures, the ones in Old World Blues level with the player.
The standard enemies in the Kingdom Hearts series of games are generally pretty manageable. Not so the special enemies in the Final Mixes. Of these, the worst would have to be the Stealth Soldier in Kingdom Hearts Final Mix. Let me elaborate on why, exactly, this Heartless sucks so bad for the non-import-gamers in the audience: First of all, he's invisible. Completely. There might be a faint shimmer, but because he's tiny, it's usually impossible to pick up on. Secondly, he's fast. Easily much faster than Sora is. Not even Stop will slow him down for longer than a half-second. Thirdly, and as expected for a Demonic Spider, he hits like a Mack truck. Three consecutive hits without a chance to heal will quickly put Sora at critical health if not kill him outright, and given Stealth Soldier's speed and invisibility, said three hits come quickly and are reeeeeally hard to avoid. For another, your one chance of keeping tabs on him—the game's target lock-on—he can throw off any damn time he pleases. The Stealth Soldier appears in the Hollow Bastion area, which, for those of you not in the know, is the game's penultimate level and stuffed with the hardest Mooks in the game. Naturally, the Stealth Soldier always appears in a crowd of these, so you can be beat up by Defenders and Wizards while desperately trying to find and exterminate (with EXTREME prejudice) the Stealth Soldier. Plus, the Hollow Bastion level is notorious for its many difficult boss fights, meaning that you will spend a lot of time levelgrinding there, meaning your chances of running into the foul beastie as much as possible are maximized. As if that wasn't enough, Stealth Soldier's appearances are randomized, so unless you have eagle eyes, you won't even know he's there until he starts killing you. The icing on the cake? If you don't kill him quick enough, he disappears, sparing you from more humiliation, maybe, but also keeping you from drops, EXP, and the satisfaction of killing the little bastard. Oh, and his drops? Have a chance of including a rare and exclusive synth item, which you will need to unlock the Infinity+1 Sword. Happy hunting.
Also in the Final Mix is the Sniperwild, a purple version of Bouncywild. They utilize lock-on crosshairs, and if they connect, can instantly hit you with a bullet from anywhere. And they DON'T STOP SPAWNING. So your best bet if you're running out of MP for Cure spells is to run to safety. They're even worse considering they will spawn unrepentantly to kill you if they see you meaning the only way to get their synthesis drop item is to rely on the short-lasting Stop series of spells. Good luck.
Kingdom Hearts II appropriately brings in two more: the Hot Rod Heartless found in Timeless River which, once reaching a certain amount of health, will start spamming an attack in which they become invincible and charge at Sora thrice. They do become trivial once you get Magnet though. The other, the Devastator from Space Paranoids, has high health, attack and defense and can 'switch forms' while you're in the middle of comboing it without warning, hitting you several times for lightning damage if you're up close. They usually come in groups of two with several other enemies. Worst of all, they are immune to Magnet.
Dancers. They have a move where they turn invincible, slide across the floor towards you at high speed, grab you, swing you around, and throw you. This move is completely unblockable and very difficult to dodge. The Titan Cup, especially the Titan Paradox Cup is made a nightmare because of the battle where you have to face three Dancers.
Coded brought us a more literal example in the form of block spider heartless, specifically the ones you encounter in Data Riku's body. You can take out several swarms of these things and still never run their spawning point dry. The worst part? they have a chance of changing into different kinds of blocks, which include metal blocks (this flavor can turn itself invulnerable by retracting its legs), bounce blocks (send you flying back with each landing hit), and danger blocks (hurts you with every hit you land on it).
The Cavern of Remembrance in Kingdom Hearts IIFinal Mix is filled with these. Every single enemy found there qualifies (well, except for maybe Perplexes, with are literal Goddamned Bats). Two of the enemies found are Recklesses and Mad Bumpers, which are stronger Palette Swaps of enemies (Devastator and Hot Rod, respectively) that are Demonic Spiders to begin with. Finally, the last area features hordes of stronger-than-normal Nobodies. The Berserkers, Dancers and Sorcerers will make you willing to snap your controller in half.
Dream Drop Distance introduces Skelterwilds, skeletalT. Rexes that can separate their heads from their bodies. What this means is that you have to watch out for both the chunks of ice the head spits out and the ramming attacks of the main body, both of which deal a good chunk of damage. They also have relatively high HP and, unlike with other large Dream Eaters, spamming Blow Off does not incapacitate them because the head will keep attacking even when the body is being immobilized by your attack. They can also grab you, stun you, and freeze you, meaning getting caught in a Cycle of Hurting when going up against them is very possible.
Aura Lions and Ryu Dragons are two other enemies you'll quickly grow to hate. The former attacks by spamming long range homing projectiles and has an extremely annoying tendency to teleport away whenever you get near it. The latter is extremely quick on its feet, attacks relentlessly, and unlike every other large enemy in the game, you can't perform Flowmotion off it to immobilize it. Both share the qualities of high HP, high attack power, being mostly Immune to Flinching and almost always showing up in groups.
This game also introduces some very annoying frog enemies with shields. They have some of the most annoying attacks in the game after the above mentioned enemies. First they have shields and seemingly randomly raise it to block you're attack commands and standard combos(Thought you were going to use meteor crash to one shot them? No one of them blocked for all three of them luckily this doesn't stop magic or flowmotion attacks.) Next, they have a nigh impossible to dodge skill that raises you're drop time effectively making you're time as Sora/Riku shorter(gets annoying when you have to finish the worlds with BOTH characters to move on at certain points in the game.) Another annoying attack they have is to combo you in the air multiple times PLUS causing burn damage to hit you on top of the combo attack you're locked in. Finally, they tend to leave about three "landmine" like attacks that also hit you then deal damage over time as well. (Luckily only the chef ones can do this it seems) Thought that wasn't so bad? They usually come in mobs of 3 or more. Mid game they're in almost every world.
Might and Magic VII plays this trope to an extreme. First, any particular breed of monster comes in three different strengths (e.g. Goblin/Hobgoblin/Goblin Lord), and anywhere a particular breed appears, the higher strength monsters have a chance of occuring. The strongest of the breed is usually roughly 3 times stronger than the weakest, which can result in an inappropriately powerful monster appearing in a lower-level area. And aside from that, many of the stronger monsters have hit effects that can include such things as "Instantly Drain MP to 0" and "Instant Death." Yes, there are monsters in MM 7 that can automatically kill you just by hitting you. If you play MM 7, you will come to loathe Minotaur Lords, Ancient Wyverns, Devil Captains, and Elder Vampires.
And then there's the spell "Dragon Breath." It's like a fireball: it explodes on contact and hurts everyone. It will probably kill your wizard and healer immediately, and even your meatshield will go down after 2 or 3. Oh, and the creatures that can use it are immune to it, so they can cast it while standing right in front of you and suffer no ill effects. And monsters in MM 7 don't have MP, they just use whatever magic spells they're programmed to use randomly. A spell doesn't count as a Demonic Spider, but any monster that can use it (Queen of the Dead, Lich King) sure does qualify.
Well, at least it's in the same vein as the previous instalment: some of the earliest enemies you'll find are Cobras. The basic ones are fairly fast, quite tough to hit (at level 1, anyway) and have poisonous attacks. That's right, they can poison party members. The one saving grace is that they've got realtively low hit points. What's that? There are two more levels of them? Oh dear...
The other enemies that tend to be rather nasty are Spectres. They're the third level of ghosts, meaning they're pretty tough. They're also really fast. And they have a chance of doing an attack that renders the target unconscious, regardless of how many hit points they had before the attack connected. They absolutely infest Corlagon's Estate, which you need to pretty much clear out to get the item you need to complete the Archmage promotion quest. Good luck with that.
AdventureQuest is usually a fun game, but Sneaks have been known to send unsuspecting players into apoplectic fits. They're nearly impossible to hit except with ranged attacks, most of which are near-useless in any other context. But even they have nothing on Xyfrags, which only take 30% damage and have thousands of HP. The slimy bastards are so much of a problem that there is a weapon with a trigger effect specifically meant to kill Xyfrag. It doesn't help that once you get to the level you will begin to see Xyfrag, the weapon becomes utterly useless. The entire fandom cheered in unison when they were made into a rare encounter; before that, they were so common it was nearly impossible for a high-level player to go through a quest with more than one random enemy without running into one of the damn things.
Also, Am-Bushes, a Lightning Bruiser with defenses even higher than a Sneak's, and without the vulnerability to ranged damage or any sort of elemental weakness. They always go first and hit so hard it isn't even funny, especially if you're using a Glass Cannon character build. Oh, and they're everywhere- they're extremely common both in random encounters and set battles in quests, so good luck avoiding them.
Anything that can drain your stats. Particularly since nearly all the monsters are level-scaled, so Level Grinding makes things worse... yet most of the equipment is so expensive you need to grind if want to be able to afford it.
You really, really aren't supposed to fight the Shadowlords in Ultima V. Upon entering combat, they teleport you to their dimension; which boxes each character in a chamber alone. They can walk through the walls of the different chambers, can move multiple times per hit, poison your characters, charm them, they hit like a mofo. And then, even if you kill one in battle, it just reforms elsewhere.
On TOP of that, if you have the Sceptre of Lord British — one of the vital items needed to win the game, and the only way to break the chamber walls — they automatically reclaim it. And you have to trek all the way back to Stonegate to recover it again. This can happen several times.
From the same game, the guards: they attack hard, quick, and in numbers. Like the Shadowlords, they are best avoided, especially if one's party members are at a low enough level that they can be killed before they even move.
In Ultima VIII: Pagan, there are kith, giant bloodthirsty spidery-things that you encounter randomly in the wild, and can kill you in one hit. And if you run into one, and it actively pursues you, RUN.
Vampire: The Masquerade – Redemption: the Nosferatu and the Tremere. The Nosferatu turn invisible at will. Attacking you doesn't break said invisibility. Unless you've bought yourself some form of heightened senses power (doubtful, since they are otherwise useless), you're hosed. And then there's the scumsucking Tremere, who are vampires AND mages. They come in big packs, and spam such lovely spells as Mind Control, Lightning Strike (aggravated damage, hits your entire party), Fireball (same, plus lasting fire damage), and the ever lovely Freeze, which does Exactly What It Says on the Tin—and high damage, of course. Did I mention that aggravated damage inherently has high chances to make your party members go berserk and start using their powers at random or, even more fun, biting the neck of the nearest person, which makes her helpless as long as the biter is drinking? That nearest person is you. Always.
Arcanum: Of Steamworks and Magic Obscura has Ore Golems. Attacking them with a weapon damages the weapon. Attacking them with your hands damages YOU. They can kill a character in two hits, can hurl stone-spells which take off two-thirds of your health, are GREATLY resistant to damage and are all but immune to firearms. What makes it worse? Most new players will encounter them at a fairly low level if they follow the main plot. You have two choices in dealing with them: spam Harm, or an Elephant Gun. The Elephant Gun is a rare high level tech rifle that you probably won't see until mid-to-late game while Harm is a first level dark necromancy spell, and the location that throws Ore Golems at you throws tons of them at you. Hope you rolled a mage. Or have electrical weapons, if you follow on that tech tree. Oh, and some of them are molten hot for fire damage.
Same goes for the Mechanical Arachnids and Automaton enemies, though these are mercifully rarer and only appear later in the story. Bonus points for the Mechanical Arachnids being actual spiders.
The worst are the Fire Elementals, which are not only stronger than Golems, but damage your armor with each strike.
Gore Guards and Lord's Slaves, or blue zombies if you will, deal fire damage. So do the void jellyfish.
Elephant Demons in Jade Empire can cause devastating shockwaves when they pound the earth, making it hard to get close to them (and demons are immune to magic). The Horse Demons also have the ability to damage your character with a fire shield when you hit them, and have a fair assortment of melee and ranged attacks.
Astonishia Story has a cave/secret tunnel that has the highest encounter rate in the entire game, and the enemies are ghosts, skeletons, and zombie-werewolf things that are nearly impossible to hit. No matter what you do, you miss more than half the time, and then they use a spell that can take out half your party in one shot. (The other half just barely survives.) Better yet, sometimes you can't run away until the third or fourth round. Unless you have smoke bombs.
Blue Dragon has the Steel-Eating Tigers. Vicious monsters that can two-shot your toughest characters (and of course, one-shot the weaker ones)? Nasty, but manageable. Until you realize that they're so damn fast that they can easily move twice in a row if they want. Be ready to revive more than a few characters when you get drawn into an automatic encounter with FOUR of them.
In Knights of the Old Republic, rakghouls, when you first meet them at a low-level. They're fast, numerous, generally don't miss, are the first time you encounter poisoning, and they are creepy. In fact, most of Taris will turn relatively simplistic enemies later on into demonic spiders. The torture droids in Davik's mansion, for example, would be laughably easy... if your only Jedi actually had the chops to use Stun Droid without them saving against it half the time. Droids in general also get ridiculous special weapons that can do a lot of damage to even the most well-armored player.
The Star Forge is full of these. Of particular note are the dark jedi and sith heavy troopers, the enemies in the middle stretch of the dungeon. Prior to this point, enemies with force powers are almost always bosses or sub-bosses, but here they show up in groups of 2-4 and respawn infinitely. Their powers can debuff you heavily and do substantial damage, and because they have light sabers they also hit hard in melee. The troopers that accompany them are relatively weak in most respects, except for one critical point: they love to spam grenades. If you're lucky they'll just use frag grenades, which do heavy damage over a decent-size area. If you're unlucky, they'll use cryoban grenades, which inflict moderate damage and paralyze everyone they hit, potentially your whole party.
The will o' the wisps in The Elder Scrolls IV: Oblivion. They're immune to normal weapons, are practically invisible when moving, and their preferred method of attacking is to absorb your health and magicka, which simultaneously damages you, prevents you from casting any healing spells, and undoes any damage you may have done to it. However, Will o' Wisps, like other specters, are not immune to the almighty power of your fists if you're a journeyman.
Trolls, too. They're fairly common in certain parts of the overworld, they're fast enough to keep up with you on horseback, they're persistent, they have a ton of health, and they do a ton of damage. Their Demonic Spider tendencies are even lampshaded by an NPC:
NPC: If you're all alone in the woods, and you see a troll coming, you run. Problem solved. Next question?
The Clannfear might also be considered under this trope—you lose health every time you hit one, so fighting more than two or three is suicide, and either way will always result in a fortune's worth of potions being consumed. Unless you toast them with magic.
The atronachs also deal damage to you whenever you want to get up close and personal. Especially frost and storm atronachs are a nightmare to deal with for melee characters, as they also have ridiculously high health.
There are literal Demonic Spiders in the the Spider Daedra. They are tough, deal good shock damage, has an ability damaging spit, and to top it off summon little Spider Daedras that do pretty much the same thing, only they can paralyse you. Did I mention that they can heal themselves?
You know what the real Demonic Spiders of the game are? Bears. They have ridiculous health, are relatively fast runners, stagger you with most of their attacks, which happen to do a LOT of damage which is not reduced much by blocking, and don't recoil from hitting your shield. They attack at a much higher rate than other enemies of comparable strength, and they attack with a lunge, so good luck getting out of its attack range.
Spriggans are incredibly tough by themselves, they can also regenerate their health three times before dying. And guess what? They summon bears.
The Scamps are really fucking annoying. Their attacks can be extremely unpredictable at close range, their fireball attacks have the uncanny ability to predict where you're going to be, and they can take a ton of hits for a weaker character to bring them down.
Above all: if you level up too much in the vanilla game every single monster becomes a demonic spider due to the fact things level up along with you. At least if you have one of the many gamebreaking items (reflect damage, resist/absorb/reflect magic, chameleon), you can ignore every enemy after level 30. Good luck reaching level 30 though.
Skyrim has a number, especially for lower to mid level characters who don't have a lot of Shout powers:
Bears are ubiquitous in the wilderness, have camouflage, and can be pretty quiet when idle. They also have huge HP pools, do massive damage, and are (much like their real-life counterparts) surprisingly agile, even keeping up with a sprinting horse. The best part? They have a great sense of smell and are always up for adventurer elevensies. Hear the rhythmical gruffing of an aggroed bear cantering towards you? Might as well do a favour and take out the Marinara sauce.
Having barely avoided dying in multiple bear attacks in the woods and mountains, the Dragonborn takes the lowland route and feels wonderfully safe for a minute before being mowed down by the furry ball of instant death ("Just add claws!") that goes by the shorter name of Sabrecat. They too have camouflage, but are entirely quiet unless actively slicing you up, and frequently come in couples. For added fun, they also inhabit snowy mountains.
Giants are docile unless you attack, hurt their Mammoths, or wander too close to their camp and avoiding them is pretty easy. Praised be the Divines, since Giants are formidable foes for any character short of a master stealth-ranger with high-end equipment. They wield clubs as long as the Dragonborn stands, and a hit from that club cannot be parried or blocked: in fact it often sends you ragdolling across the sky.
Chaurus are giant insects whose black chitin plates blend them effortlessly into the dark nooks they so love to inhabit. These critters can take a beating, spit health-draining and vision-blurring poison at you from afar, and if you can't kill one before it gets to you, you can expect to be dead in two or three bites of their mighty mandibles. For added Fun Units, they usually appear wherever Falmer are found.
Falmer are twisted degenerate elves that come in three flavours: rangers perched on hard-to-see platforms that pelt you with poison arrows, dual-wielders who can slice and dice you in a matter of seconds with poisoned weapons, and mages who specialize in combining arcane pain and your sorry behind. They are rarely found alone and will usually have at least a few Chaurus along. They build huts that provide great hidey-holes from where to stab you. They are completely silent unless they have already spotted you, and they will spot you, because due to their complete blindness they have excellent hearing. What's even better is that in addition to the usual natural caves, they also inhabit a few Dwemer ruins, where constant noise from ancient steam machinery and nasty Dwemer robot foes will only serve to double your stress levels.
The Forsworn. They don't look like much at first, just some regular humans decked out in leathers with antler decor. But they dual-wield. And those that don't dual-wield can shoot you full of ice spikes. And they come in droves. They hit hard and fast and to make matters worse, they're all Bretons, meaning they pack a powerful resistance to magic that will make fighting them hell if you're a mage. And then you meet the Briarhearts, massive Magic Knights who have had their hearts ripped out and replaced with a briar heart in a black magic ritual to give them increased strength. They are almost guaranteed to ruin your day.
Lower-level Draugr are pretty easy adversaries, but level up enough and you'll start running into Draugr Deathlords, Draugr Death Overlords, and Dragon Priests. Despite being desiccated corpses, they soak up damage like sponges, hit like tanks with chainsaws, and they have Dragon Shouts which they use to:
A. Disarm you, which means your unique Daedric weapon can end up flying out of your hands to a position where you can't ever get it back, or
B. Send you ragdolling, which means you spend over 5 seconds getting up slowly while their minions (they rarely show up alone) chop you to bits.
However, many of them do sleep in the open wearing their combat gear; if you see one laying openly supine with armor (as opposed to being naked), he is an enemy and can be sneak killed easily. Others may slumber in iron coffins and cannot be activated unless by coming close. However, they do not technically see you until the casket breaking animation is done; you can easily sneak attack them before they wake up fully.
Dragons themselves. They often come out of nowhere wherever there is open sky, usually when you're trying to do something else, and no matter how many you kill they just never stop coming. They love to flutter high in the air away from your war-axe, are quick enough that hitting with spells or arrows is pretty hard, and dive-bomb you a few times before even visiting the ground. Without appropriate shouts it can take long to reduce a dragon's health to half so that it's forced to land... and then you have to deal with its fairly quick crawling maneuvers and the fact that given the chance any dragon will chomp you up and toss you into an instant-kill ragdolling projectile towards the moons. So you adventure in the fear of dragons and level up... And once you're leveled enough to take on a Blood Dragon or two with ease, the Elder and Ancient Dragons start appearing...
Also, unlike practically any other enemy, they are impossible to disengage. Once a dragon has seen you, you WON'T be able to fast-travel away until it's dead...or you are. Better hope you're within running distance of a town to get some help from guards.
The Dragonborn DLC brings in a few nasty new enemies including the Lurkers, hulking giants that hit like a truck, it's physical attacks can stagger you, and also has an annoying ranged attack. Then there's the Seekers, miniature Cthulus, that can turn invisible, hits you with draining spells that slowly your health, magicka, and stamina, and worse of all, can create mirror images of itself that can also attack you. Oh yeah, and in Apocrypha, these things are everywhere!
Thalmor execution squads can be pretty bad. Not the patrols that just walk along until you attack them, but the randomly-encountered teams sent specifically to kill you. They consist of two Magic Knights who will chop/electrocute you at close range while a Squishy Wizard electrocutes you from further away, making it difficult to step back and regroup after they catch you off-guard. They're also a lot less common than the unaggressive patrols, meaning that if you spot tem from a distance, you'll probably assume they're unaggressive until they're already shooting you full of lightning.
Ice mages in general, if you're the melee warrior type. Most can use Ice Storm, which not only does a ton of damage to your health but to your stamina as well, preventing you from sprinting and using power attacks. It's also very hard to dodge. But the worst thing about it is that it slows you down and opens you up to even more magical pummelling.
Neither of those games can hold a candle to Daggerfall. Just about every enemy from Imp onward can be a Demonic Spider if you're not properly prepared for it, but special mention goes to Ancient Vampires and Ancient Liches, the hardest enemies in the game who will keep spamming spells at you AFTER YOU'RE DEAD.
Like in Arena mentioned below, Giant Spiders can paralyze you and get a bunch of hits in, luckily it wears off much faster than in Arena.
Arena was pretty brutal too. First dungeon in, you have to find a piece of parchment, it's surrounded by at least 7 ghouls, monsters with high defense, quite a bit of HP, and can kill you in a few hits. Especially if you're in the thief or mage classes which can't wear strong armor or use strong weapons. There are also Giant Spiders themselves, they can paralyze you getting a bunch of free hits at you. Hell if you're paralyzed while in water it's 1Hit KO and you even get a unique death text.
The random trainers in Dragon Quest Monsters have quite a few monsters that can be bothersome even considering they are supposed to match your levels, but Fang Slimes in the level sum 99-118 group take the cake. On top of being ridiculously fast, they come armed with War Cry, a skill that causes all enemy monsters to lose their next turn. It is naturally possible to have monsters that can resist this and have a chance of not suffering from this, but the game doesn't tell you which ones or how well. This is made particularly bad by the fact that various other monsters in the group like to have powerful hit-all attacks, so you're having to heal every other round except, oh right, YOU CAN'T. And the same level sum group has Bomb Crags that know Paralysis Air, which short of having monsters immune to it is capable of paralyzing all of your monsters and causing you an instant defeat. And unfortunately, they have high HP and defense so you can't kill them quickly either.
In Cross Edge, you can end up meeting Cilone, a level 190(!) enemy with insane physical dodge and crazy magic resistance. Normally, this would be a Boss in Mook Clothing; however, there's a DLC dungeon where Cilone are regular encounters. And if you thought Lujit's A-Fear was bad, Cilone's attack of choice is Ragnarok, which it will spam until it ends in a Total Party Kill.
What makes Cilone even worse is that, like Lujit and its ilk before it, it has both Parry and Pefect Barrier, negating physical and magical attacks at 25% HP, meaning EX skills are the only way to go. And for something even worse than that, they are regular encounters in the third area of the fifth world, and are buffed to level 750(!!!), meaning that unless you've some godly speed, you can't run away. Better hope you saved or you've got good defenses.
In Realmz: City of Bywater, the demonic spiders are actually demonic spiders. The random encounters in the appropriately named Spider Tower paralyze and poison when they attack, have high hit points and tend to appear in random encounters with you already forced against a wall, surrounded, in a small room. Just when you thought things couldn't get any worse, in the final battle against—yes—more demonic spiders (the writers clearly realised they didn't need a boss), a second legion of reinforcements swarm in while you're finishing with the first. (Or while the first are finishing with you.)
Dragon Age: Origins has many enemies who can pin a character down and maul them until they die, with very few ways to stop this. The first time you encounter this is a boss, where an Ogre will pick up a random party member and punch them in the face until death. You can only stop this by stunning the creature somehow, and most of the creatures that have this ability are incredibly hard to stun.
The worst of these kind of enemies are, appropriately, giant spiders. Not only can they do the aforementioned pinning and mauling, they can also tangle party members in web and some have painful venom. Good luck if you're leading your party with a mage in the Deep Roads, because they can drop down from the ceiling, web your tank, then kill your mage without you being able to use any spells at all. And mages are VERY important in this game for large encounter survivability.
That Ogre boss also has a tendency to head straight for the player character, so if you're playing a mage (IE relative Easy mode), the fight serves as the first rage-quit-hard single fight in the game. Mages also get boned in their very first available side quest, where you are sent to go take out foes who use the aforementioned stun attack, at a level where you can die in a few seconds if things are going right. Appropriately enough, these foes are spiders.
At a high enough level enemy archers start using Scattershot, which stuns your entire party and is almost impossible to resist. It wouldn't be so bad by itself, but enemy archers usually come in groups that consist of more archers who also use Scattershot.
Enemy mages. At higher levels they spam chain lightning (high damage and stamina drain against your entire party), Curse of Mortality (continuous damage and prevents healing), Crushing Prison (damage and lockdown), and Misdirection Hex (renders your physical attackers useless). They are rarely ever alone, and are often joined by the other Demonic Spiders mentioned earlier.
Worst of all is Blood Wound, which is like Crushing Prison for your whole party. No wonder everybody hates blood mages.
Dragon Age II has, perhaps to payback players who abused the insanely overpowered player mages in Dragon Age Origins, made enemy mages incredibly dangerous. They're invulnerable to damage except when casting spells, most of which they do without warning and can cause a Total Party Kill, and, unlike player mages, don't aggro every single enemy on the battlefield by casting a spell, don't get stunlocked in melee combat, and are decidedly not Squishy.
Specifically, let's talk about the Qunari mages, or Saarebas. The Qun should really take more pride in its mages, since they can KICK YOUR ASS TO PAR VOLLEN AND BACK. Not only do they take a ridiculous amount of damage, but they have a lightning ball spell that they can spam and essentially down your party within five seconds if you're not careful. Also, they can teleport, which is impossible according to in game lore on the limitations of magic.
Enemy assassins are even worse. They disappear into stealth a lot and will almost always one-shot your mages and rogues on the higher difficulty levels with a backstab that can rarely be dodged. Any encounter with more than one of them is ridiculously, unfairly difficult.
In the first game we have the Geth. They're a race of Mecha-Mooks, until you get to higher levels and encounter Destroyers, Hunters, Primes, and Juggernauts.
Krogan. Insanely tough, generally have Immunity (dramatically reducing the damage they take from your weapons), sometimes have Biotics abilities, and they love to charge you at insane speeds and get into melee range, where they can typically beat you to death in a couple of quick and painful blows. Oh, and if you kill them, they simply fall over, auto-heal all their damage, and get back up for another go.
The second game has the Collectors's special classes, which include Assassins and Guardians. The Man Behind the Man can also control one at a time, which might cause the player to have an Oh, Crap moment when the words "Assuming control" are heard. This not only fully recharges the possessed Collector's barriers but also adds ANOTHER layer of shielding and gives the possessed Collector the ability to spam biotic attacks that knock you out of cover and rip your shields apart. And the Collector constantly tries to rush you and knock you out of cover.
Sniper enemies in the first game. They don't attack very often, but when they do, it's usually with the Assassinate ability. This has the potential to one-shot characters on higher difficulties, and can even do significant damage to the Mako. As a bonus, they often look exactly like standard Mooks, so if they're mixed in with a group, you can be killed before you even know it.
The biotic attacks from the first game do very little damage, but ignore shields and almost always knock you to the ground for several seconds, during which you can't even pause the game. This is painful when it happens during a heated fire-fight, but worst when you're surrounded by nothing but biotics, who whittle your health down over two minutes while you wait for the game to allow you to access the menu.
The sequel turns Husks into these. For those not in the know: Mass Effect 2 Husks are fast-moving cybernetic zombies that tend to move in erratic patterns (making it hard to hit them) have Armor at higher difficulties (increasing the damage they can take and making them immune to many of your powers) and attack you in melee (which knocks you back and makes you unable to act for a second) in groups of a dozen or so (which staggers their melee attacks and, by extension, stun-locks you) usually backed up by either Collectors (which will shoot you to death), Scions (which shoot you with a BFG that kills your shields and knocks you out of cover so they can shoot you to death) or Praetorians ("whats this, you've taken away my first layer of defense? We can't be having THAT, can we?").
Mixed in a swarm of Husks in the second game will be one or two or more Abominations. Abominations are exactly like Husks...except that they explode when they die. And, of course, that takes away quite a bit of health. So, while you're being swarmed by Husks on all sides, you're trying to move away from the Abominations so you can kill them without being hit with... whatever exploding robot zombies are made of.
The Thorian Creepers in the first game were every bit as bad, especially as the mission where they are really swarming you is in a series of cramped corridors. The worst part is that they deal toxic damage, which completely ignores your shields. If you're playing a character with Immunity, this isn't so bad, but otherwise you're in for a world of hurt as they swarm you by the dozen and cover you in toxic vomit.
Almost as bad are the Rocket Drones. Tough to kill and with an attack that deals massive damage. Also, immune to most biotic abilities. Not too bad in open areas, but the Luna mission has you fighting them en masse in very cramped quarters. Your best friend for that mission is Tali (with possibly Garrus or Kaidan as backup). Overload, Sabotage, and AI Hacking should shut down those drones quite handily, especially if you let them bunch up in the hallway where a single Sabotage will knock out a half-dozen drones' weapons at once.
Geth snipers. They can one-hit kill you without effort on Hardcore, to say nothing of Insanity. Ditto for Geth Ghosts, which are basically the same as snipers, except that they are smaller, never ever stay still, and have a terrible habit of jumping onto the wall or ceiling over your cover to get a clear shot at you.
In Mass Effect 2, the Geth Snipers are gone, but in their place, something much nastier: Scions. They have skin so thick it takes dozens of fully-upgraded sniper bullets to bring them down (and only two classes start the game with a Sniper Rifle). While they are slow, they have an area-of-effect attack which brings you from healthy to half-way-dead in one shot, and they never attack alone. Oh, and that attack? Almost impossible to avoid and bypasses most things you can take cover behind. But good luck telling that to your teammates, who still huddle desperately to that wall as their HP is depleted in seconds. Seems you'll have to take that wave of enemies on your own now.
Go to Korlus on Insanity difficulty, especially early in the game. It's really hard, but not egregious until the end boss fight. Can you sayKroganflunkies?!
Insanity even turns vorcha into these, since almost all enemies on Insanity have some form of special defence, and even worse their regeneration can mean that you can take a vorcha mook to 1 percent, have to change heatsink clips, and by the time you've reloaded, the vorcha has already healed back to max.
Anything with a flamethrower. Getting shot by one causes Shepard to flail around, trying to put out fires on his/her armor. While you're flailing, you can't move, meaning whatever shot you is just going to get closer and shoot you again, stunlocking you to death.
Similarly, any enemy with flashbang grenades. Not only do they damage your shields and stun you, they also knock you out of cover, making you a sitting duck while the enemy unloads.
In the multiplayer demo: Cerberus Phantoms. Described as "Ninjas on speeds", they are fast moving melee flankers with biotic barriers that like to jump around and use cloaking devices to avoid bullets from long range. They prefer to get up close so they can chop you and your squadmates into pieces with their katanas. A few strikes from a Phantom's katana can easily kill even a fully shielded krogan. If standing still, the Phantom can grapple you for an instant kill, from which you cannot be revived. And although they are fragile alone (though their barriers can make up for that), they spawn in the heat of battle, while you are busy shooting at the rest of the advancing Cerberus troopers, quietly entering the flanks to drive you and your squad from cover in the best case, or single-handedly causing a Total Party Kill in the worst. So when you hear a player cry "PHANTOM!", target and kill them with extreme prejudice from long range, or chances are that someone in your squad may be seeing the Incapacitated screen/Spectator's screen very soon.
Turrets. Dropped by combat engineers, these are capable of shredding a player's shields to nothing in the blink of an eye. Engineers love to drop them in places where they can cover multiple choke points, and they sport both Shields and Armour, making them very tedious to kill. Unless you happen to be playing as an Infiltrator or Engineer. Then you can hack them to fight on your side.
Marauders become this on the higher difficulties. Their Phaeston rifles are lethally accurate, cutting through your shields like butter and slashing your vulnerable body apart during your stun animation. In groups, two of them will pin you down while a third flanks you and punches through your shields, knocking you into the fire of the other two. Oh, and they often appear with Cannibals, which will launch grenades over your cover, leaving you open to the Marauder's fire.
Banshees, banshees, BANSHEES! Ridiculously tough, can Teleport Spam, throw nearly undodgeable biotic attacks that can kill you in two or three hits... and have an instant death attack if they manage to get within melee distance. In multiplayer, you cannot be revived if you get hit with this. The scream of a Banshee is the signal that the battle is going to get ugly, fast.
If you want real frustration, occasionally there's a bug where Banshees become invisible. They still show up as a health bar when you're firing at them, but you won't be able to see the Banshee itself. This makes them even hard to deal with for obvious reasons.
3 also introduces us to the greatly buffed Geth Hunters. Unlike in 2, they turn completely invisible now, and stay invisible until their shields are destroyed. If you miss the slight distortion their invisibility makes, they will get up close, uncloak, and hit you with their plasma shotguns, destroying your shield and probably doing a fair amount of damage as well. Even worse, they like to sneak up on your while you're dealing with Pyros or Primes.
Remember the Collectors from the aforementioned Mass Effect 2? Well, as of the Retaliation DLC, they're back... with a vengeance! Now some classes can get to be a Possessed class version of itself.
Normal Abominations can explode and take a good chunk of your shields. Possessed Abominations explode as if they're in a Michael Bay movie and instantly KILL you if you're too close. Not to mention the possibility of a Total Party Kill if any other team members are too close.
Scions are back, and yes they can still shoot through cover using their grenade attacks. Possessed Scions now have cluster grenades than can kill you, and any party members clost to you, almost instantly...
They have the new Collector Captain-type enemy that can shoot Seeker Swarms, who in turn become Seeker Nets that negate your dodge rolls. Worse when you're being swarmed by enemies...
Seeker Swarms themselves definitely qualify. They don't actually damage you, but they shut down your power use for five or so seconds if they get within melee range. If you're in the middle of pitched combat when these things get to you, which you likely will be, and are playing a class that relies heavily on their powers like the Adept, Engineer or Infiltrator, they can seem like the longest five seconds of your life.
And now with the release of the Citadel DLC, we are introduced to the Cat6 mercenaries. Enemies who make Cerberus troops look like pushovers in comparison.
Cat6 Specialists not only have shields, stronger assault rifles and cluster grenades that will always manage to cover far more area than seems possible, but they also can deploy disruption drones that will instantly overload your shields once they get close enough. This can be particularly maddening during the first mission where you have very little health to work with and no medi-gel.
Cat6 Snipers are the nightmarish amalgamation of a Nemesis and a Phantom. They carry the Nemesis' sniper rifle and superior cover tactics, and have the speed and cloak of the Phantom. All adding up to one big headache for the player.
Cat6 Heavies might look like nothing more than a recolored Guardian, but where the Guardian is an annoyance, the Heavy is a far different creature. They carry shields that block armor piercing and tech attacks, have armor (thus being immune to biotics) and carry Revenants that allow them to attack from afar. They are the very definition of a No Sell. Thankfully, the omnishield can be taken down by an Overload with multi-target functionality, assuming there's a non-Heavy enemy nearby, or by Energy Drain, but without those you are not in for a fun time.
Eldar Warlocks in the Dawn of War 2 single-player campaign, who are staggeringly durable and spam psychic lightning that knocks back your squads.
Particularly Wraithguard in the Chaos Rising expansion, though, because their D-cannons will knock back anything in their blast radius, have a pretty solid rate of fire, and will knock down your squads when you try to retreat. The only good way to kill them, in fact, is to catch them by surprise and beat on them in melee with Thaddeus, where they are utterly useless.
The Mimics in Mystic Ark. Despite that you only encounter them once throughout the entire game, they fit this bill quite well. They're notable for knowing the Blackout spell, which is a much improved version of the Kill spell and has an incredibly high success rate. They also tend to cast this spell the first chance they get, so be quick with the Deathguard spell or else...
The Crazee Dayzees of the Super Mario Bros.. series transformed from slow, weak minor enemies in their debut in Yoshi's Island to tough mofos who traveled in packs and inflicted the dangerous sleep condition at a very high rate in the Paper Mario series. Particularly bad in Paper Mario: The Thousand-Year Door, where the Dayzees almost always outnumber you and will frequently put both characters to sleep before you can finish them off, which pretty much guarantees a massive beating if not death.
There is also a Metal Slime version called Amayzee Dayzees, which not only behaves similar to one (high HP, huge reward for beating it, tendency to run the first chance it gets to), but also possess the strongest single attack in the game, at 20 damage.
Another Demonic Spider in Thousand Year Door is the Spiked Parabuzzy in Chapter 6. Take Jr. Troopa's fourth form in the first game and multiply him by about 3. Per room. And you might not have the Spike Shield badge if you can't get past the retracting Spikes of Doom trap protecting it. To make things worse, the only partner to hit them without being damaged him/herself is Vivian, who can't damage them because of their immunity to fire! If you haven't equipped Hammer Throw, just run away. Or use Flurry's defense penetrating Lip Lock on them. Or use the second star special... hope you've been warming that audience up.
The X-Yux isn't encountered very often, and its HP isn't very high, but you had better kill it before it gets a turn. If it attacks, its beam will immobilize Mario regardless of if he blocks it. While Mario's unable to act or defend, it will build up its mini-Yuxes until it has four, which allows it to shoot five beams every turn. Once that happens, it's pretty much Game Over.
The Piranha Plants in the Pit of 100 Trials are a very blunt case of When All You Have Is a Hammer. They have no special tricks, but their attack of 9 adds up, especially since they often come in groups of 3-4 at a time. Having 15 HP each makes it difficult to kill them all in one round, so most players will either take a fair amount of damage fighting them, or expend a lot of FP & SP to destroy them quickly.
Almost everything in the last 30 floors of the Pit of 100 Trials. The first ones you'll encounter are the Badge Bandits, whose attacks are hard to guard against and, as their name suggests, they can steal your badges. Later, you face Wizzerds, more powerful versions of the Dark Wizzerd enemy from the Palace of Shadow. It gets even worse near the bottom, with Spunia, the aforementioned Piranha Plants, Arantulas, and Dark Bristles, which are very difficult to hit without getting hurt and have a whopping 4 defense! On the lowest levels, you'd run into Amayzee Dayzees, Poison Puffs (with the ability to store up poison, surrounding them in a cloud of unapproachability and allowing them to do a breath attack for 10 damage and chance of poisoning), Swampires (with and the ability to drain your HP), Bob-ulks (which would charge up before unleashing a self-destruct attack so that they'd be up to 16 by the time they hit—including a defense boost almost immediately in the sequence.), and the absolute worst, Elite Wizzerds—12 HP, 7 attack (8 with beam), 5 defense, and the full complement of buffs. And for some reason, they tended to appear in groups of four or five. 5 Elite Mooks at once practically amounts to a boss battle.
If you can manage to survive all of that, you'll probably find the actual boss at the bottom floor to be, ironically, less stressful.
Any enemy in Paper Mario that can attack your partner will prove to be dangerous. If Mario's partner is attacked, they cannot act for X amount of turns, which is equal to how much damage they received. A dazed partner also prevents you from swapping characters, which turns the fight into a solo match with Mario only. Things can get really hairy when you don't have your partner to help attack enemies or use abilities to buff Mario.
Status debuffs like Sleep, Freeze, Dazed, and Stop will prove to be lethal at times due to those status effects preventing Mario from attacking or defending. Any enemy that can cause such as status and starts spamming it will be one you want to kill very quickly.
Any enemy in the Mario & Luigi series which can inflict status effects besides Poison is this. The poison effect merely causes a little damage each time you make a move, but the others (Burn, Dizzy, Tripped) will leave the affected party member unable to attack or dodge attacks until the effect wears off. These games emphasize the use of quick button presses to dodge attacks entirely. Attacks that do hit the Bros. will usually take off a sizable portion of HP, so being unable to dodge at all will usually lead to a quick death. If only one brother is incapacitated, the other can usually cure him, but if both Bros. are immobilized (often by the same attack), a Game Over will be imminent.
Bowser in Mario & Luigi: Bowser's Inside Story is especially crippled by status effects because there's only one of him. He doesn't have a buddy to cure him, so any enemy that can make him dizzy or trip him must be defeated as soon as possible; one missed defensive action can mean Game Over for Bowser if the Random Number God won't let him recover.
Cocoknights from Mario & Luigi: Dream Team. They're fast enough that they're guaranteed to strike first unless you're significantly overleveled. And when they do, they attack with a barrage of annoying attacks. Sometimes they'll gather around and start spinning, requiring you to carefully move within the small moving safe spot so you don't get hit. Another attack is where they run around and two Cocoknights in a group will throw a flaming spear which if they hit will make you dizzy and unable to defend yourself from further attacks. It's telegraphed, but unless you memorize which two are the ones, you will have to strike within a split-second. And once you get down to the last few Cocoknights in a group, they'll throw their spears and run away, which has an extremely short safe period to jump. The only thing that could make them worse is if they were the most common enemy in Dreamy Wakeport and can cause battles in the overworld with their projectiles... oh wait, they do.
Beehoss. They're found all over Somnom Woods, can't be jumped on, have a fairly high amount of health and decent stats... and have an automatic counter attack ability that activates when you hit them with just about anything. That counter attack? To send out a hard to dodge swarm of bees. Their normal attacks? To send out an even harder to dodge swarm of bees. And if you happen to land on the bees mid attack? They launch an unavoidable counter attack against the character responsible. And again, they're extremely common enemies.
Mechakoopas. Common enemy, check. Decent stats? Check. Oh wait, they also have a near unavoidable attack where they charge at Mario in rows and shoot rapid fire fireballs at him, which is damn near impossible to predict and gets even worse if you've already attacked some and they're malfunctioning, which reverses their attack tells. They're the reason any player in Dreamy Neo Bowser Castle really wants to be able to strike first and destroy the main horde as quickly as possible, to avoid them using this attack until they're dead.
The Met3EX, a souped-up version of the common Mettaur virus from Mega Man Battle Network 5. It's main problem is it's ability: the shockwaves it produces turn any panel poisonous. You have about 5 seconds before you can't stand anywhere without rapidly losing Hit Points. And with 300 HP itself, you probably don't have a chip that can insta-kill one. They show up again in the sixth game as RareMet2.
On the subject of Battle Network, the second and third games feature Scuttles, which are practically demonic armored elementally-aligned deathray-shooting robotic spider viruses. It's not until the third game that they start being a problem. The green ones sprout vines that move across the field and crush you For Massive Damage, requiring obscene amounts of Button Mashing to get out of, all the while holding you still so the others can murder you; the blue ones spit guard-breaking ice cubes that clog up the field FAST; the red ones shoot fire towers insanely easy to faceplant into dodging everything else; and the yellow ones call down lightning with completely unexpected timing, which are also easy to faceplant into if dodging too fast. Oh, and the white and black ones shoot DEATH RAYS OF DOOM. And they have stronger auras. The event battle required to obtain their Virus Chip to summon one, which many players newly visiting the Bonus Dungeon will accidentally run into, will kick your sorry ass back to the surface. Oh, and they become a random encounter in the final area of the Bonus Dungeon. IN GROUPS. Beware.
Bladias in the fifth game. They have the ability to erase panels you've Liberated and turn them back to Dark Panels, plus their Darkloid attack has a good range, and these don't involve actually fighting them. The first form of a Bladia has 200 HP, and that number keeps climbing throughout the game. They can block almost anything with their sword when they aren't attacking. The actual attack can crack an entire column of panels, leaving you with that much less room to move about. Let's not talk about how horrible this is when you're surrounded and at the mercy of other viruses... Players of Colonel are less screwed as Knightman's personal Chip breaks guards and does a nice amount of damage in the process.
The Ratty virus are mouses that shoot bombs that slide along the floor and try to turn towards you like Magnet Man's magnets. What's troublesome about those mice is that they become extremely fastwhen they're low on HP. Not only that, but they always avoid standing directly in front of Mega Man. You better delete them on a single hit or you'll suffer.
Bomboy in the fourth and fifth games. They stand still for a second, before creating an explosive cube and pushing it towards you. The cube can take a lot of punishment, so you'd better have obstacle-piercing chips, or thrown bombs. When the cube reaches your side of the field, it blows up after a second, and the explosion will take up every last panel. They also have a tendency to appear alongside Goddamned Bats like Spidy and Cirkill.
DarkMech viruses in the sixth game. They can shoot out a homing ball of lightning, and while it's rather weak, it stuns you and as soon as it connects the DarkMech will teleport to you and slash you, which does a lot of damage. What makes them particularly dangerous is that it doesn't have to be their attack that stuns you; if another virus has an attack that stuns, the DarkMech can follow up after it connects.
In Tales of Phantasia golems, especially on the higher difficulty levels. They take ungodly amounts of damage, hit quite hard, can knock Cless back and stun him with annoying regularity, and bunch the party up allowing their long reaching attacks to even hit the back row casters. To top it off they are usually acting as meat shields for enemy mages who will nuke you into oblivion. On hard mode, being surrounded on both sides by golems usually spells death unless you use tricks to escape, or go all out with abilities to kill one ASAP.
In Nostalgia for the DS, Sand Worms in the second dungeon will gang bang any player walking in. They come in groups of four and each are as strong as any other enemy in that dungeon, so without copious level grinding all you can do is run.
Orcs in the Gothic series. In most RPG settings, orcs are disposable fodder-type enemies. Even the lowliest orc scout in Gothic, on the other hand, is more than a match for your character for most of the game, and when you're finally tough enough to beat the scouts down, you start to run into elite warriors.
Same applies to skeletons, which are highly competent swordmasters. Defeating a single skeleton without receiving heavy damage requires ably blocking all of its lightning-fast blows. Fighting multiple skeletons at once is a nightmare.
Most enemies that can inflict poison in Resonance of Fate. Most sources of damage to your characters deal Scratch damage, which can be healed fairly easily and only moderately messes up your day if a character takes all their HP worth of it. Poison ignores the protection that is normally offered by the hero gauge and go straight to dealing Direct damage every second or so. Direct damage is a true loss of HP, there's only one item in very limited supply that can heal you from it, and if any one character loses all their HP it's game over. The damage you take from poison isn't a big deal in itself, except that it will lock in any Scratch damage you've been taking as Direct damage as well - and the attacks that poison your characters tend to hit you for a pretty big chunk of that at the same time. You can heal from poison, but not before the first time it pings you and locks in all the Scratch damage, and the enemies will usually just do it again.
Any high-level mage in Oscuro's Oblivion Overhaul. Their AI has been enhanced from vanilla Oblivion, so they dodge your ranged attacks. They never seem to run out of magicka, so they can keep shooting very powerful spells at you forever. Spells fly much faster than in vanilla Oblivion, so they are harder for you to dodge (especially the shock spells), and every time they get low on health, they will regenerate a good chunk of it back. Even worse, due to the way OOO works, these ultra-mages con be encountered at any level, even level 1.
The Nocturne Equites in Sonic Chronicles will not only dodge almost every attack you throw at them, but counter it. That wouldn't be so bad, if they didn't do about 1/4 of your health with each hit, and heal every time too! This means attacking them will usually give them more health!
Every enemy in Heroes of the Lance falls under this category, not only because they inflict great damage and slink away while you try to hit them, but because the god-awful control scheme makes hitting them even when you are standing in the right place nearly impossible.
Soul Blazer has the demon fly. Seen in large numbers in the last stage, it is a small, fast, erratically-moving creature with surprisingly large amount of Hit Points, and on top of that, it is invulnerable part of the time.
In Hellgate: London, most players have developed a rather unhealthy dislike (read: primeval, seething hatred) for the enemies in the "Pain Leech" line, big tentacled floating heads. They seem harmless enough—damage capabilities only slightly above average, and really limited speed. Easy meat, right? Well, yeah, if you're fighting a single one. However, the danger of Leeches increases exponentially with numbers, since their lack of speed is handily supplied through their teleporting abilities, which means no matter how much you run, they're going to keep hitting you until you drop them. They also chew through shields like butter when there's more than about three of them, can cause the "phased" status (which causes you to sustain an extra 50% damage on every received hit and deal half damage) and have an uncanny ability to appear right in the middle of your escape route when you're running the hell away from a mass of missile-toting darkspawns or simply trying to find a moment of respite to recharge your skills. Taking all this into account, it's easy to see why the expression of most Hellgate players hardens when they hear the unmistakable moaning of the Leeches.
The "Bruiser" line consists of large, lumbering zombie cyborgs with maces for hands, which induce a stun effect. What makes them so broken? They're ranged and spawn in packs of 3 or more, which can leave even the toughest tank permastunned for the next ten minutes while they shoot you to death. Up close, they even have the ability to increase their defence and health regen, which just gives them even more time to set up a stun.
Then there's the "Blood Coil" line: annoying blind little reptilian beasts with suicide spikes, which induce poison or phase effects. As noted above, phasing increases damage taken and decreases damage dealt—which makes it harder to kill the next little beast that's kamikaze-ing you. Did we mention that they, like everything else, spawn in packs? And that later versions like Riftcoils can teleport and cloak?
And then there's the "Tortured Soul" line. Normally, they're blind demon shrimps that don't do anything unless you come within 20+ meters of them. They're easy pickings for ranged characters with sniper skills. Of course, when you do get close, their only attack is an unavoidable teleporting strike. Which phases. (See above.) Also, they don't target pets. And when you consider that out of the 6 classes in-game, 2 are melee and 2 are pet classes...
And the "Orbile" line, floating blobs with eyeballs. Mainly attack with lightning and self-destructing mini-Orbiles called Polyps. Defence in-game decreases with continuous attacks (claimed to make hordes of weak mobs more of a threat), and the lightning is most definitely a continuous attack. It doesn't help that damage reduction doesn't do anything, since lightning deals very small amounts of damage per tick—but very rapidly. And since 2 out of 6 classes are melee, and one of them is the resident tank, these flying mobs are incredibly hard to kill. Oh, and Polyps phase. (Notice a trend yet?) And bigger "Orbiles," called Bile Brains, spawn smaller Orbiles (Orbiles and Soul Reapers), which in turn spawn Polyps on their demise. Good times, good times...
And these are just the outright broken mobs.
X-Men Legends has normal foot soldiers that could chip off 70% of health after a single hit, and the majority of enemies that could kill you in ONE hit! Doesn't matter how many defenses you've built up, they will kick your ass.
The Force Unleashed. Pretty much any great enemy when you have to fight more than one at once. The first part of the Death Star level AT-STs and Purge Troopers and snipers all at once make for difficult gameplay. Then there are the Rancors on Felucia who take great delight in knocking you over, patiently waiting for you to get up and then knocking you over again a split second before you get control of your character back.
There aren't any Purge Troopers in the Wii/PS2 version, but the Jump Troopers and Heavy Troopers are probably just as bad. The former hovers around with a jetpack, repeatedly hammering you with rapid blasterfire and a freakin' flamethrower, and can take an insane amount of punishment (tough to hit, too). The latter wield electrostaffs that can block your lightsaber, and absolutely love to zap you in the back with electricity when you're busy fighting off the inevitable swarm of lesser foes that accompany them. And both frequently appear in groups.
The .hack series makes up for its lack of any single, solid example of this trope by making quite a few of the enemies you encounter borderline examples. Among these are the Mu Guardians that spam attacks freezing you in place until they finish, and consistently appear in groups to stack said attacks on top of each other. It's not as outright dangerous as it sounds, but every bit as irritating. It's in the third game, where Nega Guardians start showing up, that it descends into this trope's territory. Same basic idea, but those attacks are now far more damaging, and the battle is quite literally Unwinnable unless you use Data Drain, on each of them, individually... after which you must kill them AGAIN, though the second time Data Drain is mercifully optional.
Not to mention the Specters from the second game. In addition to having an annoying attack similar to the one used by Mu Guardians (though thankfully the Specters didn't spam it), they had HP that was absolutely ridiculous for the time, an attack capable of draining your SP, and an attack that was just under half as strong as the one used by Skeith (and Skeith being That One Boss on its strength alone, that is saying something). Oh, and they constantly appear IN PACKS.
Idols. They have the ability to resurrect any monsters you destroy. It gets worse when two of them are in the immediate vicinity of one another and you become forced to Data Drain one. Have fun getting through any Thunder areas in Infection, where it seems like every gate contains one.
Black Sigil: Blade of the Exiled: the pest spirits, oh dear Zodiat, the pest spirits. These little beasts have a spell that cause numerous status effect to all characters, but the most prominent one is berserk, which cause your characters to unable to take any action but doing physical attack to enemies. AND...that damn thing is immune to physical attacks. AND...there are only two items that can protect you from berserk, one is only gained from a secret character. The only good thing about it is that except for a round late in tournament, they are only found in the last dungeon, but better have Rogurd use Gold Toss or get someone with Vigil Ring / Cryptic Signet equipped when facing them or else one way or another you're going to get TPK (except if you have a weapon that can deal magical damage).
The ANBU in Naruto: Path of the Ninja. They can kill you instantly with their Silent Killing technique, enabling them to easily kill your party, and have much more HP than other enemies.
Just about everything in the iPhone/iTouch game SEED: Rise of Darkness, especially if it has ranged attacks. Lauza are particularly bad offenders, as they're listed as the same level as the almost pathetic Trampi (Level 10. Out of 99.)
Wild ARMS has a recurring gag with the Hyolkontons, Aliens with obscene hit points and their own version of Bad Breath, "Arc En Ciel".
In Skies of Arcadia and its Updated Re-release, Skies of Arcadia: Legends, there are the Slothsters. While they look like giant green sloths, they happen to be very dangerous. Not only do they have ridiculous amounts of HP and high Defense, but it also dishes out devastating strikes and a breath attack that can cause Confusion. The developers also saw fit to give it the powerful Quake spell, which does, on average, 600 damage to EVERY party member. What's worse, if you can somehow manage to whittle down this behemoth's HP, it can also use Deep Sleep, which puts it to sleep and recovers a little HP every turn.
Golden Sun games never really focus on the monsters, more on the puzzles. Golden Sun: Dark Dawn is no exception... until the Grave Eclipse, which spawns a whole bunch of monsters that, if your party is not above L30 at least, will merrily feast upon you, mostly by virtue of being powerful, quick, and hard to kill in comparison to everything you've been two-shotting up until now. In addition, Scuttler-type enemies have a vocal attack that can Stun, which they will spam, and Skorpna-type enemies have an attack, Drag Down, that is a potential One-Hit Kill. I repeat, commons with a One-Hit Kill attack. Which they spam.
Wonder Birds in The Lost Age are most likely an example, as they cast very powerful fire Psynergy, attack multiple times per turn, and are hard to escape from. To make matters worse, they will commonly get almost your entire party downed or close to it, then run away like a wuss. However, once you're strong enough to deal with them, they become a treasure trove of EXP.
The Legend of Dragoon has these in the form of Psych Druids. God help you if you get these things in the red and don't finish them off before they get a turn, because they'll happily drop a psych bomb on you (effectively the strongest non-dragoon magic in the game, as well as being all-hit and non-elemental.) if you're looking for a way to run yourself out of angel's prayers and healing mists/rains that's the way. Beyond that, any mob that can do a One-Hit Kill (Death, Professor (also full of Standard Status Effects for extra "fun"), and some other annoying ones)
Arx Fatalis has Ylsides, which appear human but are extremely fast, hard-hitting, and well armored.
The blue blob enemies from Ys III. These things hit extremely hard with a wide hit-box, and can kill you outright if you're not leveled (or equipped) properly... which you probably aren't at that stage of the game.
Worse are the spear-toting enemies in the Cursed Mine, whose weapons have greater range than yours and deal massive damage. And you need to conserve your HP and ring power for the boss.
Darkstone features goblin bat riders. They have an inordinately high amount of hitpoints; their attacks are fast, accurate and powerful; they are immune to all elements except fire and they can spawn bats.
Drakensang has its share of tough enemies in both games, including Harpies, Giant Crabs, Emerald Spiders, Stone Golems and Fire Spirits. The first two are severely annoying, as they can easily inflict wounds on your characters via physical damage, and it only takes five wounds to kill your character. Golems have a lot of health, are super resilient and hit like trains, and are immune to wounds. Fire spirits, while still manageable, have the irritating quirk of setting ablaze all characters around them.
The more advanced versions of the Bholdoms (wild boar-type creatures) in Ys VI, who not only hit hard and can take a whacking, but also inflict debilitating Standard Status Effects''. Also, the cave scorpions (Gilchas) in Mythos Path and Limewater Cave.
Musyamon in Digimon World 3 start as this. They are in the Gecko Swamp, with the only other digimon there being, well, Geckomon, who besides one obnoxious attack are pretty weak. Musyamon, though, have ungodly high offensive stats for any digimon at that point in the game, when your team will likely only be around level 15 or so. Also, thanks to the annoying escape mechanics, it's almost impossible to get out of the battle before it uses one of its strong attacks on you. Naturally they become a cakewalk once you level up properly, but until then, good luck.
The Dark Spire. Nearly every floor has at least two elite enemies. Nearly all of them are this, and there are some more common enemies that also qualify. Being a Wizardry clone this is normal and expected.
The best examples though are anything with a breath weapon. Breath weapons do damage based on the HP of the user to the entire party and can be used in the surprise round. It is not at all unusual for later ones to kill everyone before you can move.
Baten Kaitos Origins has Machina Auto-Turrets, which are found all over Tarazed, and are one of the biggest reasons it's That One Level. They're fast, tough, have powerful normal attacks and a special attack that hits the whole party, and come in groups of two or three.
Also in Tarazed, you find Prima Queens, which hit way too hard and explode after three or four turns unless they're killed. Just to add to that, they often appear with Dance Kings (which hit like tanks) and have a combination attack with them that takes off unreasonable amounts of health. Encountering two Dance Kings and three Prima Queens at once practically adds up to a full on boss fight. Frigid Queen's Festival won't save you if Guillo gets knocked out two turns in.
Any enemy encounter with a combination attack could really count, given that they usually hit like a freight train made of lions.
In Icewind Dale and its sequel Icewind Dale II, you'll find many of these:
Mummy: Unlike their Baldur's Gate counterparts, they can cast flamestrikes. You face them as early as chapter 1.
Salamanders: They have either cold or fire auras and always come in large groups. Their auras even damage you when they're non-hostile toward you!
Umber Hulks: Looking straight in their eyes will confuse you if you fail your saves. They're also backed up by Minotaurs.
Demons Souls is hard as it is, but nearly every skeleton enemies in Shrine of Storms is a walking Demonic Spider waiting to kill a newbie player. Not only their rolling attack waste stamina even on block, they're very fast and agile, spawn in numbers, and the archer variant fires White Bows which deal magic damage. Not enough? The Black Skeleton variant wieldsdual katanas, and while it has a very crappy turn radius to be abused, it is resilient and very deadly. The Gold variant uses large machetes that double as shields, even more durable, comes in pairs, can take off huge chunks of HP in a hit, and usually found guarding treacherous passes where if the skeletons don't kill you, the fall will.
Fittingly enough, The 7th Saga has literal spiders that appear right at the point where the game's Fake Difficulty starts going through the roof. The damage they inflict is insane, and they can poison you.
In Lunar: Dragon Song, many common enemies, plus a few bosses, can steal or destroy your your equipment, accessories, weapons or items. Since you either have to spam card effects to prevent this (cards of which you'll have to battle tons to farm) or constantly re-purchase or regain missing goods (which involves farming money or the item in question), Save Scumming is generally advised.
In Assassin's Creed: Revelations, the damned Janissaries. Let's review: They're literally the only non-boss characters that can survive a counter-attack or killstreak (multiple ones at that!). They can only be one-hit-killed when caught by surprise (they can shrug off multiple crossbow or bullets at point-blank range) or when at least 5 chain-kills have already been achieved. They can hold their own against Ezio AND his Assassin recruits when everything else that goes up against him usually winds up dead within seconds. They can block or dodge endless numbers of Ezio's attacks and have an unblockable ranged attack that can slice off large chunks of your health. They can run faster than you, making it impossible to just leg it when they show up. And they WILL show up, because at least one shows up in almost every single group of guards. And in more than one mission you have to go into a camp full of nothing BUT Janissaries. It's like someone just designed an entire enemy class that was Ezio-proof. And then put them everywhere.
Hellhounds from Dragon's Dogma are probably the epitome of this trope. You encounter them very late in the game, but that doesn't stop them from being the most aggravating enemies in the game that even seasoned players still end up having trouble with. They don't stagger very easily, so it'll take a few hits before you can actually make them flinch or knock them down. They do NOT sit still, and run all around the place in an effort to confuse you. Their attacks have no problem stun-locking you or knocking you down, as they possess a long range fire breathing attack that will hit for lots of damage and most likely leave you on the ground. But that's not all! While you are on the ground, they can take a hold of you and drag you off somewhere. They can either throw you off a cliff (if it's too high, you die), or bite at you for massive damage while you shake them off. Finally, they come in groups of no less than three. Yup, these guys are mangy mutts from hell.
The Secretaries from OFF. They're easy to avoid, if you're not looking for 100% completion, but otherwise, they're tanky, they hit harder than anything else at their level, they pile on the status effects, and they can show up in groups of three. Also, they look like giant babydolls.
Dish Turrets in Epic Battle Fantasy 4. They can stun multiple characters at once and force them to miss turns, they can Syphon multiple characters at once (which blocks off all of their skills and reduces them to basic attacks and items, the latter of which you'll promptly be using to cure the condition, thus wasting more turns), and can dispel your entire party's buffs at once, in a game where Useless Useful Spell is emphatically not in effect and you really need those buffs. They also have a ton of HP, so you can't expect to pick them off easily. While their attacks have low raw power, this is hardly any consolation considering they just about always have other powerful enemies fighting alongside them, who will happily abuse the free turns the Dish Turrets are providing them to blast your characters into the stratosphere. Always go after the Dish Turret first. That is, of course, assuming they don't come in pairs. Or groups of three. Or alongside the resident Boss in Mook Clothing.
And they're the first of the four types of giant machines in that area. One Defender by itself deals enough damage every turn to keep YOU on the defensive. Thankfully, there's usually only one at once, and it's the only giant machine the boss can't summon, but the one encounter with two at once is one of the hardest encounters in the level and one of the hardest one-wave encounters. Laser Turrets aren't so bad, but Fridge Turrets will wet your entire party, making all of you weak against their own ice attacks and the Dish and Laser Turrets' thunder attacks for several turns.
Golems can also count as this, to an extent, largely depending on the difficulty (since the biggest difference between difficulties is enemy stats). There's nothing gimmick-y about them; they just hit really hard and have lots of HP and high defenses. And unlike the Dish Turrets, which only appear in the factory, there are many varieties of the Golems, so you'll often see some version of them regardless of the region you're in at the time.
In the previous game, Monoliths were perhaps the strongest enemies in the game. Viking Monoliths could freeze multiple party members at once, Ancient Monoliths could stun party members, and both could deal massive damage, but Cosmic Monoliths would have to take the cake. One won't hesitate to use a Dark attack easily capable of Total Party Kill every three turns, while unleashing weaker attacks, weakening you or buffing itself, or charging said attack even stronger in between. One functions as the effective Mini-Boss of the last main dungeon, but more appear in the short true final dungeon (often more than one at once). In this game, they've been greatly nerfed and the Cosmic Monoliths removed, but enough so for the Viking ones to appear one level earlier than they did last game (Ancient Monoliths didn't appear until the last dungeon). Also, this time there are two new kinds: Undying Monoliths, appearing in a couple of side areas unlocked after level 3, and Sky Monoliths, which only appear near the end of the last dungeon (just before Ancient and Undying ones make a reprise).
In the last game, Turtles (then known as Eaters) and Elementals could've counted too, but now they don't stand out among all the other guys, and are mere ants compared to one newcomer...
This game, despite nerfing the Monoliths, added the most Demonic Spiders yet, the dragons. They have tons of resistances and few weaknesses (and if you face two different kinds at once, may not have any common ones). Not to mention they have powerful sweepers and even stronger single-hitters, can buff their entire party and debuff all of you to massive extents, and in some cases can even heal or kill instantly.
Any enemy in the Exile/Avernum series with level 6 mage spells or greater is this, because they can summon Demons at will. And those demons can not only breathe deadly fireballs, but they can also summon Devas and Shades. And those Devas can summon other monsters in turn. One high-level mage can potentially fill up the screen with summons in only a few turns, which is why they are usually your number-one priority to kill first. Unfortunately, they themselves like to stand in the back ranks of the enemy party, and are usually resistant (if not completely immune) to your spells.
One of the most frustrating enemies in Bravely Default is quite possibly the dreaded Myconid. Sure, how could a sentient mushroom be so bad? The Myconid has a downright unfair ability called spore, which activates whenever you hit it with a physical attack. What does it do? MAKES ANOTHER GODAMNED MYCONID! This isn't some pale clone, its another complete freaking monster. And they have pretty sizable health, so its very difficult to one-shot them at this point. Using magic doesn't trigger the ability, but MP is pretty low at this stage and you can easily run out, not to mention ethers are pretty rare and you are going to end up burning through them pretty quickly. The battle can drag on for quite a while, since you kill one, move on to the next and it creates another in its place, which can really wear you down. However, if the battle drags on for long enough, you can end up getting tons of bonus money and EXP, which somewhat makes the battle nearly worth it.
In the same boat as Myconids, another annoying creature to battle is the Cerberus in the Vampire Castle. Whenever you attack the Cerberus with a physical attack, it counters with a move called "payback", which dishes out MASSIVE amounts of damage right back at you. And this triggers EVERY single time you hit it with a physical attack. To put it into perspective, payback typically dishes out 1K of damage. At this stage in the game, your HP is probably around 3-4K. And Cerberus aint no slouch. He's got 5,000-ish HP, pretty decent speed and is ready to dish out the pain at every turn. The worst part is, it doesn't take up its turn, so after you get nailed with a payback, it can go and attack you for even more damage. Whilst magic again, doesn't trigger the effect, you'll find that its typically far less useful than physical attacks. Multi-target attacks also don't trigger payback, but they're typically not as powerful. And just because the game hates you, there's a chance to encounter 3 of these bad boys at once in the higher floors. Hope you stocked up on phoenix downs...
In Wasteland 2, anything toting grenades rapidly becomes this. Explosives cannot miss, ignore cover, and deal flat damage that ignores armour in an area of effect. Since gameplay naturally leads itself to bunching up your characters behind cover and focusing fire, anything that can half-kill every single party member with a single attack (especially since they have an infinite supply of explosives) becomes a primary target. And once you hit Los Angeles the game starts throwing rocket launcher enemies at you, which don't even have the courtesy of short range and will instead snipe your entire party for 100+ damage from halfway across the map.
Burning Beetles in the first dungeon's third floor. They are random encounters, can move twice per turn, have a powerful normal attack, Maragi, a crowd-hitting fire spell, and Thorn Chains, an attack that can seal your magical attacks, although the first time you encounter them the attack will probably kill you instead. All dungeons have an extra-strong giant monster random encounter, but this one stands out because of how weak you are when you encounter it for the first time.
Justice Swords, also in the first dungeon. When you first encounter them, their normal attack hits hard, and they also have a poisoning and a paralyzing strike.
Beastly Gigas in the fourth dungeon. They have two attacks: Brain Shake, which has a chance of putting its target to sleep in addition to doing medium damage, and Heavy Shot, which deals heavy damage that pierces, so one character in the back line will get hit in addition to one in the front. These attacks are not that devastating by themselves, but they have a chance of attacking twice in one turn as well as high HP, which means that you'll need to spend a lot of SP if you want to kill them before they wear down your party.