Fallout: New Vegas gives us bark scorpions. They are fast, tend to come in groups of two or more, and will actively try to flank you. They will jump, either to close the distance or for a quick escape, and their poison is horrifyingly potent (and causes an Interface Screw to boot). The only thing keeping them from joining their radscorpion cousins in another trope altogether is that they don't hit particularly hard, nor are they anywhere near as tough. Still, if you are low level, and you get stung with no antivenom on you, you are pretty much dead.
There's also those damn Nightstalkers. They aren't particularly dangerous, unless you have the misfortune to stumble across a pack of them, but they're fast, difficult to hit, and make a horrible hissing noise.Later on, they become invisible. The only saving grace they have is that their blood, tails, and eggs are worth a lot of money. Their brethren from Old World Blues, however, are straight up Demonic Spiders, partly because of their Level Scaling.
Geckos in general (though Fire Geckos, Golden Geckos and Green Geckos can be Demonic Spiders depending on your level) they are easy to kill, but they are very fast and usually try to swarm you.
Bloatflies, giant mantises, and giant ants are generally nothing more than minor annoyance, unless there are a lot of them. The Zion Mantises from Honest Hearts, however, are upgraded to Demonic Spiders.
Dark Cloud 2 has Gemrons, little baby dragon enemies with different elements. At a distance, they stun you with fireballs; at close range, they roll towards you and knock you down...and then they spit fireballs a split second after that. The regular bats aren't nearly as annoying.
...unless you're going for a "Defeat Enemies With Items" medal, at which points you'll be damning those high-flying, nigh-unreachable bats quite often. And loudly.
Or a "Defeat all enemies using only Max's right-hand weapon" medal. Max's weapons can deflect fireballs, and they count as a magic/gun attack. The only GOOD thing one can say about Gemrons is that once you get the Gemron badge for Monica, and level up her monster forms, you can have a LOT of fun flying around dungeons in Gemron form blasting enemies away with fireballs.
Old isometric action-adventure game Nox had some truly frightening bats, especially for players without area-effect attacks. In online play, several Conjurers could band together with four bats each, creating a Warrior-wasting bat-tlegroup.
Dragon Quest and other games of its type pretty much burns an unpleasant association with the phrase "Slime Summons Reinforcements!" The worst offender of this was Shining the Holy Ark, where you could start with enemies A, B, and C and have cycled through the entire alphabet before killing the last one.
And don't forget the Bell class of monsters, who appear in large groups, summon more bells and other monsters...and certain types of Bells, once they've gotten 8 or so of them on-screen, either play a level-up song or an instant-kill song...
In the NES games at least, with insane random encounter rates, EVERYTHING was either a Goddamned Bat or a Demonic Spider.
The cliff racers in The Elder Scrolls III: Morrowind. Annoying because 1) they're everywhere; 2) they can keep up with you even if you max out your speed, acrobatics and athletics stats; 3) you can't sleep when a cliffracer is near; 4) it's nigh-impossible to fight them in melee unless they are facing you squarely. If you played an archer, though, cliffracers made wonderful pincushions - once you grow accustomed to the wrong hitbox, which adds the annoyance of having to shoot at their legs to hit their torsos.
Amusingly, in Oblivion, you can hear people discussing "Saint Jiub, who drove the Cliff Racers from Morrowind". Jiub was a fellow prisoner on the ship at the start of Morrowind, never seen again in-game. There's also the drunk who sings about them.
In the Dawnguard expansion for Skyrim you actually run into Jiub in the Soul Cairn, who gives you a sidequest to collect pages for his Opus, which basically describes, in heroic detail, a fierce battle against an entire brood of cliff racers.
A pestilence was creeping across the ashlands, a menace with an insatiable hunger that plagued innocent travelers simply trying to get home. It was my self-sworn task to hunt them down one-by-one and drive them from the skies. Their fury knew no bounds and their war cry resonated across the land. They were the notorious cliff racers, and they had to be destroyed.
So many people hated cliffracers that in the PC version of Morrowind, someone modded a downloadable "cliff racer killing ring," that when equipped, automatically killed any cliff racer who came within 50 yards of the player with a "zap!" sound. There are other mods of this sort, including some that make a lot of sense, such as one that removes all cliffracers (useful, but creates a scarcity of cliffracer plumes, a potion ingredient), and one that modifies all non-diseased creatures to be nonhostile to the player (including cliffracers). Since normally in the game, virtually anythingis instantly aggressive towards the player, this is a welcome change.
Slaughterfish are an aquatic version of this trope.
There are more wolves in The Elder Scrolls V: Skyrim than have ever existed in the history of the planet Earth, and after a few hours of exploring, you will have littered the landscape with their corpses. The fact that their pelts aren't worth very much only makes them more irritating.
Skeevers, which are basically giant rats, are barely more than a bump in the road for even a level 1 character. What turns them into Goddamned Bats, however, is the ridiculously high chance they have to give you a disease.
The dragons themselves, by about the point you're attacked every single time you exit a town, are just challenging enough that you seriously consider missing out on the open world you bought the game for in the first place and just fast-traveling everywhere.
Some of those damned archers and mages in Dragon Age: Origins. It doesn't help that the difficulty is rather inconsistent, but generally, these two are the most annoying types of enemies you'll face. (Friggin FIREBALL!!!)
There's a few fights towards the end of the game where you have to fight groups with archers using Scattershot, and a ton of guys with shields who spam shield pummel. Yeah. Those are fun.
Whenever you're trying ot hunt a Hyren in Magi-Nation, you'll run into these.
The SNES game Soul Blazer has two varieties of bat-form Goddamned Bats that try to circle you in swarms just beyond your sword-reach and swerve to strike if you ignore them and try to walk normally. And they can fly through the walls.
They however become much less of a problem once you get a certain low cost rotating spheres spell that suspiciously conveniently circle around you at about the same range that the bats circle you.
Soul Blazer is also one of the rare games where one might be incited to proclaim "Butterflies!''"
Heck, the game is full of non-bat Goddamned Bats. You've got jumping caterpillars — in fact, several types that only move into your sword range once you get in a spot where they're gonna hit you. You've got giant flowers that put out tiny bees that you practically cannot kill until they get you — very hard if you're trying for a no-damage run. There's dragons that leap out of the water at you with no visible sign that that's an area to watch out for. And then there are the non-spawned guys whose only purpose is to make killing the spawned guys that much harder, and who are unkilled whenever you return from freeing another citizen — the pillars of fire that spit fireballs at you are slightly annoying, but the freaky face statues that conjure up icicle death in your path, that's somewhat more than merely annoying (because you would be perfectly safe from the forewarned icicles conjured 2 spaces away from you... if you weren't trying to lunge at bats and sorcerers).
Quest for Glory IV had an enemy which combined the Demonic Spiders trope and this trope. BADDERS. Spider-Bats with poisoneous attacks which flew at you one at a time so you could only attack them when they were swooping at you, so that meant that the only time you could make an defense was when THEY were making an OFFENSE.
This is counterbalanced by the fact that, unless you're a fighter, there's no automatic Badder fight at the beginning of the game. Also, you're given direction on where to go, the forest you're stuck in is not all that big and poison both works very slowly (it will take an hour of real time to kill you, while traversing the forest takes about five minutes if you don't know where you're going) and eventually heals itself for weaker forms of poison. Finally, the enemy encounter rate is turned way down until you reach the town for the first time (in fact, the only way you can possibly get into a fight is to go looking for one, that is, straying between screens for a long time), and after about five minutes of real time, the sun comes up.
In Quest for Glory V, you have the badders' long lost cousin, the batties. No poison this time since they're bats, but their small size, high speed and large numbers make them annoying as hell. Worse, they only show up at night or in dark places, making them very difficult to spot until it's too late.
Neoshadows, Darkballs, and Defenders in Kingdom Hearts: Chain of Memories. All of them are fond of using high-level cards (8s or 9s) that will stun you if you try to hit them with a lower-level card. The former two are also prone to chase you, which can lead to you running away while you look for a card that will stop them. Neoshadows are particularly annoying, both because they travel in swarms (so you end up getting repeatedly pounded after a single card-break), and because they can flatten themselves against the ground to avoid your sleights (normal Shadows can do this, too, but they're much weaker).
Kingdom Hearts II provides you with various Nobodies; such as the Berserkers and Dancers, both of which boast impossible-to-block attacks; the Samurai, who boast a reaction command that requires a very fast reaction time if you want to avoid getting damaged by it instead; and the Assassins, who self-destruct in your face if you don't kill them fast enough.
Still in II are those fucking undead pirates. They are rather easy on their own, but what makes them annoying is that they are invincible to any attacks unless they are in moonlight. It's incredibly easy to accidentally knock them right out of the moonlight mid-combo, and some areas have a lot of shady spots, meaning you'll be constantly pushing them out of the moonlight, forcing you to wait until they step out of the shade. The Japanese and Final Mix versions are even worse in this regard, as fire attacks set them ablaze and cause them to run around erratically, a trait that was censored in the US and European versions.
Kingdom Hearts: 358/2 Days manages to be even more annoying than the enemies listed above, with the Emerald Serenade Heartless. It's incapable of attacking and only being able to move on a set path.... But it always runs away, is rather fast, and has a boatload of HP, making it an extremely annoying enemy to kill. Oh, and at least two missions require you to kill it. One of them is in a fucking maze.
Basically all the Wonderland Heartless count as this. There's ones that teleport when you hit them, ones that teleport you when you hit them, one that causes random status effects, one that emits a poison that can EASILY kill you if you try to attack it. They all fly too. And they all appear in the aforementioned FUCKING MAZE.
Birth by Sleep continues the long and glorious tradition with the Mandrake Unversed. At long-range, they'll constantly pelt you with wind slashes which can stun-lock you while you're dealing with its buddies. A couple of these guys can keep you stun-locked practically forever. And when you try to close in on them they'll either poison or confuse you.
If you think about it, the majority of the game's enemies are designed with this trope in mind. Scrappers are designed to hang back & attack during lulls in combos; Shoegazers become invincible for a period if not beaten quickly enough; Spiderchests burrow and poison you; Archravens fly high in the air, grab treasure prizes, and attack anything they touch when doing so; Blue Sea Salts can freeze you; Chrono Twisters cast stop; Axe Flappers attack with projectiles & feign being stunned (also, they're batlike). Oh, and of course, being Kingdom Hearts enemies, they swarm you like crazy.
Hell, this dates all the way back to the first Kingdom Hearts as well. The Large Bodies (which have appeared in just about every game) may very well qualify, because they block any blow you deal from the front with their disgustingly incredible fat, so you have to strike them from behind. Depending on which game you're playing, this can either be laughably easy or a gigantic pain in the posterior (I'm looking at you, 358/2). The aforementioned Darkballs were also just as annoying as they were in CoM. At one point, you have to fight an entire group of them (during the Final Boss, appropriately enough). Then there were those damned monkeys that ran circles around you and could very much overwhelm you early on, especially on Expert Mode. And the Nobodies mentioned above? Not the only Bats in KH2. There were the freaking flying zombies that chased Sora everywhere, the Crimson Jazzes that are literally impossible to run away from, even with maximum movement abilities, and surround you with exploding fireballs, the Toy Soldiers and Graveyards, the Morning Stars, the... you know what? Let's just say "Kingdom Hearts is the best example for Goddamned Bats" and leave it at that.
Practically every Nightmare in Kingdom Hearts 3D has something about them that can make them one of these, whether it's spamming a move that inflicts Standard Status Effects, randomly breaking out of your combos, and/or keeping you staggered with multi-hitting attacks, on top of being a heck of a lot more aggressive then enemies of the previous games in general. It's far easier to name the ones that don't have some manner of annoying quality to them. On the plus side, said annoying qualities can be turned against them once you create their Spirit counterparts to use as party members.
The Imp enemies in Disgaea appear designed to drive players into a rage. They have very long movement and jump ranges, and their Hell Pepper attack deals surprisingly large amounts of damage and poisons survivors.
Imps are also one of two monsters with a healing special, which uses a separate targeting algorithm from attacks. allied/neutral units. Unfortunately, it still counts as an "attack" for the purpose of turning neutral Dark Assembly monsters against you...
The enemy Thief and Kunoichi classes in Disgaea 2 can lean towards this. As no matter how many thousands of levels above them you are, they still land their status moves on you almost 100% of the time while your own tend to fail about half the time. Little is quite as annoying as having a lvl 4000 die because two lvl 10 kunoichi poisoned it and put it to sleep at the same time. Prinny Dance comes close for the same reasons but it actually tends to miss or at least not always inflict an affect if the hits fail to do damage.
Of course, the bright side of this is that almost every unit used against you can be used by you. And yes, it is satisfying to inflict three different status effects on one bigass enemy.
The Imps were replaced by the much less annoying Mothmen in Disgaea 2... only for the Mothmen to become Goddamned Bats themselves in Disgaea 3. Thank goodness we've never seen both of them in the same game, huh?
The Ambling Pirates in Disgaea 2 definitely qualify for the "appearing too often" category. To get to the best endgame areas, you must encounter and defeat 16 different kinds of pirates for their unique map pieces, all of which will appear at random in the Item World (randomly generated levels you can go through to make equipment more powerful.) It's frustrating as hell when you're down to the last one or two kinds and two out of every three encounters is with this guy, especially considering that its more likely to find pirates the more map pieces you have.
The Poison Lilies in Phantasy Star Online. Not only do they spit out the titular poison, they also can paralyze you, making you unable to do anything but use items. Ob Lilies in the Ultimate difficulty level are even worse, spitting out the instant death technique Megid. Oh yeah, and they can still paralyze you.
In fairness, Poison Lilies are a joke once you get to know them. Goading a Lily into trying to peck you but failing is a trivial affair, and while it's doing that you can simply shoot at its friends - the pecking lily will never stop trying and failing, and once its friends are dead you can turn your attention to rapidly attacking the pecking lily before it has chance to paralyse you. In addition, armour upgrade units which prevent paralysis are not difficult to acquire, and poison is probably the least annoying status effect in the game once you reach a decent level.
And then in Episode 4 in Blue Burst there's Zus. Large pre-historic looking birdlike creatures that fly around, dive bomb, and shoot Frickin' Laser Beams from their mouths. Not quite as commonplace as most other Bats but still very annoying. They fly around very fast and are unhittable while they dive bomb you (Unless your clever or have Gifoie), which always knocks you down and sets you up for another hit, or preparation to be mobbed.
Oh, where to begin in Wizardry VII: Crusaders of the Dark Savant...
How about with Fish? Red Piranhas and Piranha Sharks are about the only things you'll meet out on the ocean, come in large numbers, don't give much exp, and hit decently hard.
Or Birds. Spectral Crows blink in and out of existence randomly, meaning magic is unreliable, ditto your heavy melee weapons. They also like to inflict fear on multiple characters, giving them a chance to run away from combat. Dragon Rooks breathe acid on multiple characters, fire crows breathe fireballs, and vampire vultures hit fairly hard, have a lot of hit points, and can drain maximum hit points-from which there is no recovery.
Moths, too. Spectral Moths do the same thing as spectral crows, while other moths enjoy blinding, poisoning, and paralyzing party members.
Ghosts-virtually Metal Slimes. Very resistant to magic, can inflict all the worst Standard Status Effects, can hit hard on multiple characters when they wish, and like to vanish when low on hit points.
G Rattkin. Fast, appear in large numbers, and can usually do a lot of damage before the AoE spells clear them out.
In Wizardry 8, any large gathering of monsters (usually eight or more) can turn into a Goddamned Bats scenario, since fighting them is often extremely time-consuming, and they all get to attack...
Not to mention the fact that if you scare them away they high-tail it into the distance leaving you stuck in combat whilst you try and catch them because you can only get out of turn based play once they die!!!
The Spiteful Crow is another infuriating enemy that was found very early in the game (and twice more after Onett) — they were faster than you (and were quite evasive), and could steal one of your items!
The Territorial Oak could be annoying (exploding trees, anyone?). But at least it usually showed up alone, so you could speed through its death message to end the battle before it killed you.
Another enemy in the same area as the Territorial Oak is the Mobile Sprout, which fits this trope to a T. It can heal with Lifeup, it can suck away your PP with PSI Magnet, and it can create more Sprouts. At this point in the game, you only have one party member, so it can get very annoying fighting them.
More or less any enemy that can inflict status effects. If they can do it, it will very rarely fail and they're surprisingly difficult to get rid of.
The worst are mushroom enemies. They are often fast enough to go before the party gets a chance to kill them and inflict a status effect that can't be gotten rid of without trudging all the way back to town. The "mushroomized" effect combines a chance of randomly attacking a party member with Interface Screw that makes walking back to town to cure it a chore.
In Mother 3, "brooms" appear near the end of Chapter 2, at the end of a dungeon filled with enemies that are kind of annoying to kill because you gotta use PK Freeze to kill one at a time. Anyway, the brooms are relatively easy to get by since they move in a pattern, but they lure you in with items! And if they catch you, they sweep you off your feet and you land in a garbage can all the way at the beginning of aforementioned dungeon.
Worse are the Tiny Lil' Ghosts in Earthbound. They can randomly freeze, posess or damage one of your party members each turn, and can only be removed if that member faints or goes to a healer. Fortunately, they only appear when certain ghost enemies try to attack, and can even be killed by the possessed party member.
Mass Effect 1: Thresher Maws are frustratingly time-consuming and boring to kill. What's particularly pernicious is that, when they appear, they sometimes spawn directly under the Mako, killing you instantly without warning.
Normal Mooks sometimes did this by charging straight at you, even if they had sniper rifles or machine guns. Irritating, as you have to get out of cover and turn round before you can kill them.
Any biotic mook with Warp in the first game. Usually no stronger than their buddies, but they knock you to the floor with a very hard-to-avoid power while their allies fill you full of holes. They also repeatedly shout I WILL DESTROY YOU to put more salt in the wound.
Husks are also annoying and tough to fight in large numbers. In the first game, they love softening you up with an area of effect blast of energy that kills your shields, giving them a distance attack in addition to the old flailing arms. Bad enough when they were in a massed horde, even worse when paired with geth: The former requires you to remain constantly on the move, while the later requires gluing your butt to cover.
In Mass Effect 2, this gets pushed to Demonic Spiders levels when they're accompanied by Scions, for the same reason as the Husk/geth combo. At least now only some of them explode.
It gets worse in 3. Husks can now grapple you, forcing you to mash the melee button to shake them off. This is annoying at the best of times, and fatal when it knocks you out of cover into heavy enemy fire.
Geth hoppers can jump from surface to surface effectively instantly, and do it a lot. Fortunately, they can be targeted with biotics rather easily.
In Mass Effect 2, Harbinger can quickly reach this status. He's not so hard as to be boss caliber, but he's constantly rushing your position, knocking you out of cover, and even if you kill the body he's possessing, he'll just take over another. This form is redundant.
LOKI and FENRIS mechs too - although a few well-placed shots can make them explode on each other.
Guardians in 3. They're only dangerous at very close range, but if you don't have any biotic squad members, a sniper rifle, or anything that can punch through shields, then you'll just be trying to pop them through the slots in their shields or flank them.
Averted for infiltrators, who find them easy prey. Not only are infiltrators good at sniping Guardians through their slots, but Guardians also move slowly.
Mass Effect 3 has one for every type of enemy you can fight against in the multiplayer cooperative mode:
Cerberus has Combat Engineers, who are relatively easy to defeat as they don't understand cover, but they can drop a turret which will eat through your shields like nothing else, and they love to put them at choke points.
Unless someone has the Sabotage power, which allows you to briefly turn a turret to your side.
Geth have Pyros, who have very short-ranged flamethrowers, but are completely implacable and have lots of resistances due to their Shield/Armor mix (you can't hack them without taking both layers of protection down, for example).
Reapers have the aforementioned Husks. They also have Marauders, who are individually easy as even their shields are pretty pathetic, but when they're around other units, even out of sight, they will boost those units with special armor that you have to shoot through or around in order to injure the unit affected.
And now the Retaliation DLC is set to bring back Abominations (those exploding Husks we mentioned) and Scions. Alien gods help us all.
In Shining Force, the Giant Bats, and their later incarnation, Seabats. Each is a flying enemy with a large movement range and higher Agility than other enemies for that part of the game (meaning your attacks are significantly more likely to miss). The original Giant Bats can even randomly put your characters to sleep with a physical attack, making them skip at least one turn.
Shining The Holy Ark — many, many creatures could call for reinforcements or duplicate themselves in some way, making random encounter battles go on for 10 minutes or more. Bear in mind these aren't boss battles. Saying that, a couple of the bosses had endless mooks appearing to help them out.
The World Ends with You has a few of these. Among them: Goddamned Bats that are fairly difficult to hit in combat, Crows that steal your pins during combat (disabling that attack until the crow is killed off), Porcupines that drop exploding needles on the battlefield, and Jellyfish that, on harder difficulties where you do less damage with attacks, can often be very difficult to kill off-they summon more of themselves, often faster than you can kill them.
Don't forget Elephants that spam ridiculously long-lasting stomp attacks that do no damage but interrupt whatever action you're currently in progress of performing, even if you're floating a good 7 feet off the ground and the actual footprints that spread out and cause the stun effect are several inches in height at best.
No damage if you're not getting hit by the attack itself, you mean. It's freaking painful if you don't avoid them, especially if you're playing at level 1 to boost drop rates. Also, the interrupting "whatever action you're currently in the process of performing" is worse than it sounds because there are a lot of attacks that take more time to ready than the stomps allow for.
And Pigs; while harmless, they run away from battle in seconds unless killed quickly.
And Taboo Noise, which will actively seek you out during a scan.
And Frogs, who latch on to your characters and attack, and will absorb either short- or long-range attacks depending on their color, along with Shrews that plant deadly bombs and launch drill-like attacks at your characters, and burrow underground to make themselves more difficult to hit. The former is especially a pain in the ass because not only does Joshua get knocked out of the air if he is hit, but he has to come back down to the ground to dodge them.
And the Sharks, which eat other noise to make themselves stronger and hide under the ground while you're trying to hit them so you have to guess where the hell they're going to pop up.
The second expansion pack of Neverwinter Nights gives us Duergar, or dark dwarves. Every single one of them has the ability to cast improved invisibility, and every single one does so the moment they realize that you're there. And the worst part? They're the second most common enemy in the campaign. The loading screen tips weren't lying when they said that you were going to die often.
At the epic level ranges where the expansion is located, you can have an overabundance of spells and - even better - artifacts giving you true seeing, rendering their little trick useless to begin with.
Duergar were also in the original campaign. This was a pain because a) an entire region would spawn NOTHING BUT SQUADS OF DUERGAR, and b) if you'd reached a certain level they'd hit you with Phantasmal Killer. What does this do, you ask? Unless you pass your Will and Fort saves, it does Exactly What It Says on the Tin. Having to respawn 10 times per level because the Random Number God leads to a handful of bad saves? Does horrible, horrible things to your money and XP.
In Paper Mario: The Thousand-Year Door, the Crazee Dayzees, which tend to pop up on narrow pathways, making them hard to dodge — and should you succeed in slipping past one, there'll be another a little further along, leaving you trapped between two. In fact, the whole turn-based fighting set-up of the game turns all the minor opponents into potential time-wasting Goddamned Bats — although they are useful for Level Grinding.
Towards the end of the game, you actually run into bats, which swoop down from the ceiling and are very hard to avoid or get an initiative hit on. There's also a chance that one or two bats will spend the resulting battle attacking from the ceiling (instead of hovering like most flying enemies), where Mario can't jump on them. I hope you remembered to equip Hammer Throw or Quake Hammer...
In the first two Paper Mario games, there are ridiculously annoying little creatures called fuzzies. They suck your health, can split in two, and have really hard to time action commands. What's more, they're everywhere and are among the hardest enemies to avoid. Be warned.
However, use of the Zap Tap badge renders them unable to damage you, as it electrocutes enemies that directly touch Mario; the only way Fuzzies can hurt you. But they're still annoying, because they will keep dividing. As soon as you kill one, another will take its place...
The Shroob Rexes in Mario & Luigi: Partners in Time. The irritating thing is that you CAN'T jump over them if they do that "charging at you" attack if they haven't been stomped at least once or twice to squish them down to a more appropriate height; and the worst part is that, with their high attack and speed, ou won't be able to strike first nor will you tell which enemy in the overworld WILL have them on their team.
Hermite Crabs (and their recolours) in Mario & Luigi: Dream Team. They take at least two hits to take down because of their 'hide under rocks' gimmick, can't be defeated instantly through a pre-emptive attack thanks to the same gimmick... and are ridiculously common in Wakeport and parts of Driftwood Shore. Oh, and god help you if you want to try and beat the Expert Challenges involving them, since you have to also dodge their (extremely annoying) attacks perfectly.
Viruses. They come in huge packs... outside of the Dream World. Their gimmick is like in the game they originated- get three of the same color to touch and they instantly die. However, getting the exact color needed to clear out several of them is difficult and comes down to memorizing which order of color they change when hit. When they attack, they go on huge parades which require you to hit them in just the right order... or else get barraged by a crapton of Viruses that slow, lower defense, or even shrink (basically, weakened attack and you can't use Bros Powers). When their ranks are lowered, they start moving towards the Bros. in a way that the camera just can't show right; get hit and you end up tripped (complete paralysis until hit again). They also have a crapton of defense, so once you get down to a few rows that just aren't in the position to be cleared, have fun whittling away.
Bandits. Their basic attack will steal 100 coins, and if you don't kill them within a few turns, they run away and it's lost. Then they start using decoys that will do huge damage and most certainly dizzy if you hit the fake. They also come in packs of 5 or more. They also have a lot of health.
In the Dream World, there are Spinies, which take an annoyingly long amount of time to kill because, well, they can only be hurt by hammering them then jumping. Eventually they get up the same turn you hammer them, and their only attack takes absolutely forever to go through. If that wasn't enough, sometimes a Lakitu will appear, which can make even more of them appear.
In the earlier Ultima games, Gremlins EPITOMIZE this trope. They're small, attack (usually) in packs, and on their own don't do a lot of damage. Doesn't sound like much, until you realize they steal food from the party. Food in those games served as a counter for how long the party could stay in a area — run out of food, the party starts losing health until they either reach a town or die. So, Gremlins could steal ALL your food — condemning your party to a slow death if you couldn't reach a city in time.
In the turn-based online RPG DragonFable, any mushroom-type monster is ridiculously hard to hit. This gets even worse when they're level-scaled.
The Minx Fairies are incredibly aggravating — if you manage to get them down to less than half of their HP, they'll Full Heal themselves, which costs them only one MP. If you don't stun them or drain their mana so they can't use the move, you're in for a long fight, especially on the higher levels when they have about 200 MP. And worse, they're strong to Light, unlike just about every other monster in the game, making one of the two most powerful weapons of the game useless against them.
Gothic: Minecrawlers. Minecrawlers. They have pretty nasty damage considering the stage of the game where they're first encountered, but wouldn't be nearly as bad if they weren't... well... in the mines. Which means that you're in a confined space, which is occasionally dark, with blind corner after blind corner, plenty of fatal dropoffs, infinite opportunity for them to sneak up behind you and to top it all off nicely, the "helpful" NPCs that would otherwise be looking after you have no idea how to climb ladders and so end up running in circles while the minecrawlers eat your face. Oh yeah, and did we mention they're giant, hissing, screamingants?
In the Might and Magic series, from the point battle started to be open as opposed to having "battle-areas" (like JRPGs), that is, from M&M 6 onwards, any enemy in great quantity could surround your party and start to plummet you. The best skills you can use against them, that is, area damage effects, will also affect your party, and you're down to using less effective multiple projectile spells like Poison Spray or Spark. The worst of the lot, you guessed it, are Goddamned Bats (and Rats), who have the annoying habit of diseasing or poisoning your party members, rapidly deteriorating their stats and health unless you have some pretty advanced Body Spells or alchemic potions (which are fairly wasteful mana-wise, the first, and rare/waste of ingredients for other potions, in the later.)
Seiken Densetsu 3 has the line of "Dark Priest" enemies. All of them are spellcasters who love to spam Healing Light. The Necromancers in the final dungeons are the worst of the lot, responding to everything with at least one casting (usually two) of Healing Light that heals them for over 400 health. They have 800 or so and you can do about 400 with one move if you're lucky, and can maybe hit them with two before they respond with Healing Light if you're really lucky. What's really annoying is that they don't even attack. They just continually cast a spell that drops every aspect of your ability to deal damage, making fights with them nigh unwinnable unless you can clear the effect. Oh, and they usually spawn in rooms that trap you until all enemies are dead.
Insidious Maya in Persona 3 are a prime example. Unlike most other Maya, they don't have any offensive skills. Instead, their skillset was designed to make them as annoying as possible. They know Diarama, which will generally heal themself or an ally to full health, Life Drain, which also keeps them healthy and Eerie Sound, which inflicts Distress on the whole party, making them more vulnerable to critical hits. Which, in Persona 3, grant the enemy an extra turn. This wouldn't be so bad were it not for their tendancy to show up in groups of five. If you get a preemptive strike on them they're not so bad, but if they get one on you things can go From Bad to Worse very quickly. Worst-case secenario: Eerie Sound hits everyone and you're stuck in a constant loop of getting critted, knocked down, then getting back up only to be knocked down again. They're weak to Ice, but when there's so many of them the chances of missing one and ruining your One More chain/chance for an All Out Attack are VERY high. And then they'll just start healing again. Not the toughest of enemies, but among the most irritating.
The Tigers in the second dungeon of Persona 4 spam the an all-party-damaging attack and seem to constantly critical hit your party. On top of that, they take a LONG time to kill. It's possible to spend at LEAST fifteen minutes on one set of two.
The trick to the tigers, at least in their later appearances when you have more levels, is that Yosuke's Tentarafooalways hits them with confusion, which happens to disable enemies quite thoroughly.
Brave Fencer Musashi had some of these too. In underground dungeons there are some bats among the other enemies, who are just IMMENSELY annoying: they move randomly, are pretty hard to hit due to the weird camera and they follow you through the floor (so you can't simply run away from them).
Monster Hunter has the Cephalos and Cephadrome, which swim around in the sand faster than the player's sprinting speed, with only a very small fin exposed for the player to (hopefully) hit. And then there's the Monoblos and its relatives, which have an annoying habit of burrowing into the sand and staying there, thus being undetectable by any normal means. If you lose track of a Monoblos and have no extraordinary means of locating it again, you're hosed. Thankfully there are countermeasures which can be used to somewhat ameliorate the annoyance posed by the above monsters.
And don't forget the Cats. How to grief another player: kick a cat and bugger off sharpish before all its friends show up with bombs.
The Bullfangos are basically boars that travel in groups and will charge you the instant they see you. Getting hit by one will send the hunter flying. Whoever thought of delivery missions with parcels that break if you drop them should be beaten. Whoever thought of Bullfangos should be shot. Whoever thought of putting Bullfangos in delivery missions should be beaten, shot and beaten again for good measure.
Don't forget Vespoids, the flying wasps. Most times they only do just a small amount of damage, but they can sometimes paralyze your character causing him to fall down for about 20 seconds and twitch on the ground helpless. And in most cases, this is going to be just before a wyvern of some sort decides to charges at you turning you into a hunter pancake. It's less dangerous but still just as annoying, when you get paralyzed while carving or trying to harvest items as well.
Throughout Wild ARMs 3, you encounter a variety of owl monsters. The ones earlier on usually do their worst by simply being airborne enemies, meaning that it's slightly tougher to hit them overall, inflicting Disease on your party, and stealing an item that usually isn't too hard to replace like a Heal Berry, but the ones later on do all of the above, but when they steal, they steal and run, meaning if they successfully steal that precious Ambrosia or 2 you've been saving for an abnormality whore, then they're gone for good.
Spiderweb Software games:
In the Geneforge series it was the Vlish, flying tentacled creatures with ranged attacks that had effects that made every combat longer; either stun, terror, poison/acid, some of them could even heal their allies. They ran to call on the assistance of others, came back to swarm in packs, then ran away when taking too much damage. And throughout the series, many entire zones were dedicated to these damn things.
In the Avernum series it was the Imps, who were not nearly as bad, less frequent, and the rewards were better. They also assembled in packs, used ranged mental effects such as stun, charm, fear, and ran away at low health.
In The Witcher, Drowners (and their improved counterpart drowned dead). They're no threat to the player unless he accidentally runs into them early in the first chapter, and can be killed in seconds en masse. What makes drowners a pain is that they are still all over major locations in chapters 2 and 3 (the swamp and sewers), take longer to loot then kill, and simply force you to kill them before you can end combat.
There is a special item that makes them flee when equipped (and the ring slot it takes up has no other items outside of signet rings, a mechanic used 3 times in the entire game, and a similar item for wraiths), but it is a Power Up Let Down and makes them WORSE. What makes them so annoying is that during combat, you can't interact with items (such as opening a chest or door). The item keeps the drowners at a distance that STILL keeps them in combat, and keeps them too far away to instantly kill in group style.
Baldur's Gate II has its entire first dungeon filled with Mephits, Fire Mephits, Air Mephits, and Mephit portals. Goddamned Bats indeed.
Any creature with level draining abilities becomes this, easily. Most of them aren't really *dangerous* damage- and health-wise, but they'll drain your characters to dry husks in minutes and take away your high-level spells. Most players quickly learn what things makes you immune to level draining, and uses scouts equipped with said immunity when vampires are afoot.
At higher levels, Baldurs Gate II hands you two "all bats must die" spells, Cloudkill and Death Spell, both of whom insta-kill low-level pests and are very good at cleaning out entire rooms full of Goddamned Bats before your fighter has managed to close with them. An otherwise Demonic Spider called the Umber Hulk is also extremely weak to these spells.
Any enemy with an activable shield in Zoids Legacy. You usually have to waste at least two party members' attacks to bring the shield down, plus the user can still attack through it. Fortunately, when these become common, the party should be strong enough that they do not become Demonic Spiders.
The .HACK//series of games has a few. The standout performers are Killer Bees and Mimics, both of whom are difficult to kill and spam negative status effects. In the words of Black Rose, "Confusion and Charmed are the worst!"
Let's not forget those resurrecting statues. If you faced two of them at a time (which you often did in the later levels/games) they would continuously keep reviving each other, forcing you to Data Drain one of them.
Any enemy with a "Evading" attack in Sonic Chronicles and high attack. And any enemy that you need to have "Piercing" to do damage to. And enemies with a high Defence. In short, around 30% of the enemies in the game probably qualify for this status.
Geckos in Fallout 2. Those damn things are everywhere. Thankfully, a few of them tend to be nonhostile unless provoked.
You'll be encountering raiders for the whole game; they're everywhere, they're aggressive and they're always hostile. But they never switch away from light equipment, so they turn into Goddamned Bats as soon as you get some XP and basic armor. At higher levels they're essentially target practice, but you can never ignore them because they'll start combat turns and force you to engage them or flee.
In random encounters, wolves also have a habit of circling your party and mauling you to death, especially at lower levels. Luckily though, they're unable to do much to you once you've reached a high level and got some decent armor.
Grand Chase features Harpies: starting from Kerrie Beach towards Marsh of Oblivion, your life will be made miserable by these flying creatures, even more so in Champion Mode, when they're buffed with all sorts of goodies. And then they make a grand comeback in the Battle for Bermesiah as Violent Harpies. What fun.
The Slimes in Odin Sphere's Titania level. They don't take a lot of damage from normal or Psypher attack. But the worst part is that if you don't get away, they will cling to you, and stick you in place, dealing their damage, while opening you up to attacks from Wizards. Generally a Napalm will kill them, but good luck if you don't have the stuff to make one, or had wanted to save them for a boss.
Dokunemons In Digimon World 2. Those guys are weaklings who'll probably die in a single hit. However, they can use their signature move to become untargetable for a few turns again and again and again and again... That being said, you can get that move if you manage to recruit or fuse one.
Bone Buzzards from the Nobilia/Crustacea region in Secret of Evermore. They do practically no damage, swarm in from EVERYWHERE, and can only be hit if they're really close to the ground. The buzzards, however, can hit you no matter how high they are. They also have no delay behind their attacks, and can hit you again immediately. When one makes contact, your attacks are immediately canceled even if it would have hit and killed the damn thing. Your only choices to deal with them are either to dance around for god knows how long, or waste spell ingredients (which is always pure overkill).
Bat type enemies in Star Ocean: The Last Hope quickly become this. They attack in packs, can fly (making them a hard target) and often cause the Fog Status Effect (the character can no longer aim or automatically find the enemy). Worse than them are the Bees, who attack in larger packs, move faster, are the second to third monster encountered, have an amazing ability to target the physically weakest character (usually Symbologists) and are the most responsible for many broken bonus boards. For those who want to know what a bonus board is, it's very useful, very hard to build up and is reduced either totally or by half with a single critical hit on the leader. No more 140% EXP bonus for you!
Amoebas in Drakensang. The least problem with them is that they make you stink. Then, there's the fear effect that stops your character from attacking them for five seconds. You can gang up on one and carve it up with little problem, but at times, they attack in packs, effectively gangbanging you to death. Just two can waste your whole party, especially if you go melee on them. Oh, and they regenerate. FAST.
Thankfully rare in Vampire: The Masquerade- Bloodlines, but when you go to fight the plaguebearer Bishop Vick, he has zombie minions. They take several attacks to kill, they are literally endless, and while they're not fast, they can latch onto you and render you completely unable to do anything else until you throw them off. The best way to deal with them is to run past them, knocking them out of the way with a blunt weapon such as the baseball bat or truncheon, get to Bishop Vick's room, and defeat him as fast as you can. The implication is that without him around to feed them, they die of the plague and starvation.
There's a perfect example in the first boss (arguably a mini-boss) in Ys Origin. One of it's attacks is turning into a swarm of Goddamned Bats and chasing you around/moving in your path to swarm and bite you. It's made worse when the monster splits into two and has one of them swarm you as said Goddamned Bats, while the other tries to attack you with magic or some such. The bats they turn into are even an enemy you can find shortly after the battle!
Breath of Fire II gives us the Beak. When you first encounter it it's as the first boss of the game when your character is solo and pitifully weak, but at roughly level 30 it starts showing up in the hunting areas— and it's still just as strong. Curb-Stomp Battle ensues. So why is it on this page? Because every time you encounter one in the hunting area, you get kicked back onto the world map. No big deal, just avoid... wait, is it chasing after you? At speeds much faster than you can manage? Yes, these things are Too Dumb to Live and will actively commit suicide by your party, preventing you from getting any of the drops you actually went in there for. If you try going after it using the hunting area mechanics, it proves nigh-impossible to kill this way. And if by some miracle you do manage to do this? Another one shows up. And it drops absolutely nothing. Once these things start showing up in your hunting areas, you'll probably never use a hunting area again.
Any variant of the Shadowcats in Labyrinth of Touhou. When you first face them, they will be faster than anyone in your party, even Chen. They also know Shadowstep, which hits your entire active party and, more often than not, paralyzes at least half of them. This leads to trouble if you have to fight two at once and you can't get Meiling, the only person who can cure paralysis at this point, out on the field.
Later in the story, the bats are replaced for at least one day by rats instead. This is actually plot-relevant (unlike the bats, which are just annoying) because it's a sign that something's wrong in the sewers.
The Blighttown Giant Mosquitos in Dark Souls. Always flying and thus hard to hit in melee, so weak as to be a waste of a spell, an attack that's not too troublesome on its own but can shatter your guard if there's more than one(and there usually is) that also help cause poison, to help finish the infliction if the poisonous waters of the swamp didn't already. And to top it all off, they don't give you any souls and they respawn indefinitely.
The Dark Spire. One of the most common early enemies? Literal Goddamned Bats. Most of the other common enemies early on are also Goddamned Bats in the figurative sense. Then you run into the bats that look almost exactly like the first kind but are actually Demonic Spiders...
The TerraTerrors in Terra Tower, the penultimate dungeon in Chrono Cross. They're everywhere, actively chase you, and have a tendency to spawn Cytoplasms in battle, which endlessly use weak techs. At this point, none of the enemies can damage you enough to be a real threat, so getting into fights is tedious and pointless. It doesn't help that the game is suffering from serious Ending Fatigue at this point; these fights only serve to drag out an already-tiresome Marathon Level.
Terraria has literal bats, but most of these (save the ones in Hardmode that confuse you) are fairly tame. The actual Goddamned Bats are spellcasters — monsters that teleport at will to anywhere nearby, and can shoot their projectiles through the wall and love teleporting to places you can't reach without tons of digging. Thankfully, most projectiles can be swung at with a melee weapon or tool to get rid of before it hits you, but still. Trying to mine Hellstone in The Underworld is especially annoying when Fire Imps keep pestering you every 5 seconds, especially when there's lava everywhere. Once you actually close the distance with one of these bastards, they die quickly and easily and tend to just stand there while you smack it to death. The only problem is that another one will spawn in just a few seconds....
Tyrant Abaddon in Shin Megami Tensei III: Nocturne's final dungeon. They resist all magic, counter physical attacks (and cast a spell to become effectively immune to them if they ever get a turn) and have a large amount of HP and as a Tyrant, you can negotiate with them, but they give out half the EXP of other, easier to kill, foes in the same place. They aren't strong enough to actually kill anything that is at full health though.
Infinite Undiscovery has green baby giant spiders called Larva. They are either in packs or jump off of the corpse of its parent that you just killed. They can get incredibly annoying because of their ranged attack (and in this game, even that attack can stagger you and interrupt your attack) and the fact that they can easily and quickly swarm you. They are only really bad in the part of the game where the hero is briefly separated from his allies.
Dragon's Dogma has harpies and their advanced form, succubi. Individually, they can be taken down with one or two well placed attacks, but good luck getting them off. These creatures fly, sometimes erratically, cast sleep, can knock you down, stun, grapple and do flat out dive bomb attacks. To make matters more interesting, they tend to spawn in groups and have no qualms about harassing you in the middle of a miniboss or full boss fight.
Parasite Eve has especially annoying actual (mutant) bats fluttering around in the Chinatown sewers, capable of reducing your attack range to zero with a sonic attack, and mutant crows that constantly move and peck away at your HP, dropping only piles of junk when killed. That junk can be put towards earning extremely powerful weapons, however. You'll just have to kill 300 crows to get enough.
Pararoids and Metaroids in Mega Man X: Command Mission. They're very fast and hard to hit, and while all they use is their regular attack and one ability, that ability is Parasite, which sacrifices themselves to raise another enemy's stats to the max. There's always at least two of them in a given encounter with them. Metaroids are even worse because they don't even have the regular attack; as soon as they get a turn, they use Parasite. Which they will most of the time because they're the fastest enemy in the game. Meaning that you have to be able to kill them before they can take a single turn. If you do manage to kill them, you'll find that they drop...absolutely nothing.
Every enemy with a ranged attack. Since they can't be blocked, those can chip away at you while you deal with their tougher, melee buds. Of course, nothing stops you from simply running to them.
Nymphs. Very hard to hit, moving constantly all over the place and peppering you with projectiles. They can also summon additional enemies that, while not really powerful, still annoy you and require to be killed... and she can always summon another ones.
Tougher undead block most attacks flawlessly, have a few deceptively long-ranged unblockable swings and take a while to die. The toughest version can also summon additional undead to aid it.
Though early on they're Demonic Spiders, Minions in both forms quickly degrade to it, for better or worse. They're very adept at blocking and interrupting your combos and are durable enough for even an end-game hero to take a while to finish off with magic.
Trolls are normally fought mano-a-mano, but in these few occasions they have a back-up(of, conveniently, Minions), they become this. Their attacks can't be blocked and will knock you down, leaving you vulnerable to getting swarmed. They also take a while to kill.
Etrian Odyssey IV has Goddamned Vampire Bats in the last leg of the final dungeon-they can't do much in the way of damage, but they can drain HP, have enough health that they can CONSTANTLY call in another bat just before you can finish the last one off, and to top it all off can team up to perform a skill that drains a massive chunk of TP from everyone in your party when there's three of them in battle. And for maximum irritation, they can also be accompanied by a beetle enemy that can sponge all attacks directed at them! At least both the beetles and bats are weak to electricity so a multi-hitting electric move will get rid of the beetle in a jiffy, but that can still give the bats a turn to call in reinforcements or do their TP-draining move.