Stone Edge is an inversion. Since its introduction, the move has been distributed like candy to many, many NPC trainers and Pokémon. It's Rock-type (one of the best offensive types), has 100 base damage, and a high critical-hit ratio, but it has 80% accuracy and low PP. Stone Edge missing will cost you a game, or at least some serious momentum.
Gen I Amnesia is this, since there is only one Special stat, covering both Special Attack and Defense. This means sharply increasing the Special stat back then is like using two Calm Minds in one turn. Note that the Psychic-type of Gen I is assigned to the Special stat. Trying to counter them with a physical attacker is difficult since they usually have poor Special stat to hold out in battle.
In Gen. I, if your Pokémon is slow enough, "Ekans used Wrap! Ekans's attack continues!" Again and again and again. This was fixed in the later games. Wrap no longer holds your Pokemon to keep it from attacking.
On the other hand, this nerf made Wrap relatively useless, since the damage on its own isn't anything to write home about. It does prevent the target from switching out, though.
Wrap can still annoy the heck out of you in the Pokémon Mystery Dungeon games if you're slow. Lileep loves this move in particular.
The foe's Clefable used Metronome! The foe's Clefable used Volt Tackle! It's super effective! Gyarados fainted!
This has been changed in later games to be dependent on level - the higher the level the attacker compared to the target, the more accurate it becomes. 30% is now the minimum, with an additional 1% per level difference.
On the topic of attacks hitting more often than they should, Hydro Pump, Blizzard, and Thunder are notorious for not always hitting. However, the computer will always hit if you're at all weak to the attack.
In Generation I, while the other 120 BP moves had 70% accuracy, Blizzard, for some reason, had 90%. It was brought in line with the other moves in Gen II.
Stealth Rock. It creates an "entry hazard", which means that any further Pokémon who switch in will be affected. At least Spikes and Toxic Spikes could be dodged with a Flying-type or somebody with Levitate... but not Stealth Rock. Unlike dealing a set amount of damage, like Spikes, it factors type matchups into the damage done. This means that someone who is weak to Rock loses a quarter of its health, and someone with a double weakness losing half, just from being sent in. It's absolutely everywhere.Entire teams have to be made just to survive (and use) it. It's the only reason anybody uses the otherwise pathetic move Rapid Spin (there are even specific Pokémon whose sole reason for usage is to use Rapid Spin). It's made many Pokémon weak to Rock seen as unusable (mostly). The metagame, when it doesn't centralize around weather, centralizes around this move. No other move is as infamous or game-changing as Stealth Rock. It was so bad that close to the end of the fifth generation, there was an unofficial gameplay rule instituted on certain battle simulators- OU ('standard' gameplay), with one change: Stealth Rock is banned. Many considered it a very welcome change.
Pokémon X and Yfinally gave this move a nerf by making Defog into an unblockable Rapid Spin that works on all sides of the field, to the celebration of many, many battlers. While it's still present in the metagame, Defog makes it much easier to use 4x rock weak Pokémon like Talonflame, and Stealth Rock is no longer something that you can set up first turn and forget about.
Any Psychic-type move, but especially Psybeam, Dream Eater, and Psychic. Unless you're using a Dark-type, watch out. Wait, you're playing Red, Blue, or Yellow? Sucks to be you! "The foe's Alakazam/Mewtwo used Psychic!"note In Gen. I, though it can easlly OHKO anything without explicit resistance.
Earthquake. Sure, it's a move with good power and great typing and accuracy. However, said type is one of the strongest in the game. But that's not what makes it so bad; what makes it bad is the fact that it is absolutely everywhere. The chances of a high-skilled team not having the move are slim to none, and an immense amount of 'mons can learn the move. It also hits everyone that isn't immune to it.
Wild Voltorb used Selfdestruct! Or worse: Shiny Graveler used Explosion! Koffing/Weezing are notorious too...though a Ghost as your lead or Rain Dance nullifies it.
Whitney's Miltank used Rollout! And if you're playing HeartGold? Miltank used Stomp. *insert Pokémon you're using here* flinched. Even if it's a Ghost-type, due to Scrappy ability.
On that note, any move that can cause Pokémon to flinch. For every tale of glorious victory by causing the enemy to flinch, there are several others mourning the loss due to having a 'Mon flinch at the wrong time. One of the most annoying could arguably be Fake Out which 1) Is a priority move and 2) always flinches, wasting a turn.
Any attack that causes confusion, particularly Confuse Ray. Since The Computer Is a Cheating Bastard, the next 5 turns will have your Pokémon "hurting itself in its confusion". Naturally, that's only true for YOU, as the computer will snap out of it in 2 turns and won't hurt itself once. Confuse Ray makes it worse: it's 100% accurate, and pretty much every trainer with a Zubat, Golbat, or Crobat has this attack on it, and will be more than happy to use it on their first turn.
The foe's Shiftry used Swagger! Swagger, while not 100% accurate, also causes confusion. It also doubles the target's attack. So, in the event that you hurt yourself, you'll do twice as much damage to yourself as normal. And the damage boost stacks. Oh, and anyone that can use TMs can use it! Fortunately, if your mon has the confusion-preventing Own Tempo ability, it simply gives them a free Attack doubling. If not? Good luck. It's even worse when combined with Foul Play, which uses the target's Attack stat instead of the user's to deal damage... and that includes any stat increases.
Cotton Guard, for anybody who relies on physical attacks. It raises Defense by three stages, which essentially means that a mere two turns of use maximizes Defense. Which means a 400% Defense boost. This basically means that, unless you get lucky enough to get a Critical Hit, even super-effective attacks will do Scratch Damage. Oh, and guess who can learn it? That's right, Whimsicott!
In Gen. I, anything with Poison Sting. The AI has an irritatingly high chance of poisoning you if you don't KO the opposing 'mon within a couple turns, sending you straight back to the nearest Pokémon Center.
Double Team. There's a reason why it's almost universally hated, and if there are any moves that people agree to ban from a battle, that one's right at the top of the list. Worst of all, the AI gives that move out to their Pokémon like Halloween candy and it has a tendency to make even your 100% accurate moves miss after just one use.
Protect, while not nearly as bad as the others, is still really annoying and makes you waste a turn and PP. If the AI at least used it strategically it'd be one thing (since you could still counter it with the attack Feint), but since it's purely A.I. Roulette they end up using it just because, even when it's obvious that you've already won and it won't help them thus they just delay the inevitable. The problem is that no one in their right mind would run a moveset with Feint on it, especially with the nerf. It now deals 30 damage (at least before, the damage of 50 could be bumped up to 75 with Technician), but now, even if you factor in a STAB and Technician, you aren't going to be busting 70 power with it. Meanwhile, its only use is to defeat Protect and Detect, both of which are not worth the trouble. Shadow Force, the only other attack that can counter Protect, is only available on Giratina, so if you don't use legendaries, good luck.
Thankfully, Gen. VI introduces Phantom Force; sure, it's the nerfed version of Shadow Force, but a handful of Ghost-types (andYveltal) can make good use of it.
Watchog used Retaliate! note Retaliate doubles in base power (from 70 to 140) if a Pokémon on the user's team fainted in the previous turn, and when you factor in STAB, that jumps up to 210. No, really. This move can be found on the second leader's Pokémon, and if you're not ready for it, Lenora will plow you like fresh snow. Thought you will force away Herdier and take down Watchog first? Herdier has Retaliate, as well.
The foe's Clefairy used Encore! (and now you're stuck on one move until you run out and only have Struggle left. You might be able to wait it out if you can switch out, have enough PP on your moves, or if you've got some PP ups, but if you happen to be on your last Pokémon...)
The foe's Wobbuffet used Encore! (Same as above, only now switching isn't an option. Now Wobbuffet can either wipe you out with Counter Attack or switch to a teammate that can set up on you while you're helpless.)
In multiplayer games where items are allowed to be used, a Nidoking can easily turn into one of these back in Gen. I. One-hit KO moves have an accuracy of roughly 45%. X Accuracy makes it always hit. NIDOKING used FISSURE! It's a one-hit KO! Repeat four more times, and you will still have six Pokémon to one when you lose all PP.
If there's one move that trainers dread seeing Zebstrika use, it's "Flame Charge". This is because not only is Flame Charge super-effective against Grass-type Pokémon (which normally have a resistance against Electric-type attacks), but it also boosts Zebstrika's already very high Speed stats. Oh, and it loves to spam this move several times. This means that now it is insanely fast and can easily strike with moves like Spark, Thunderbolt, and Charge Beam several times (and paralyze your Pokémon with said attacks) before you get a chance to do much damage.
Audino/Minccino/Clefairy used Attract! Your Pokémon is in love! Your Pokémon is immobilized by love! What's worse is that unlike moves that cause confusion, Attract doesn't wear off after a few turns. You have to switch out in order to cancel out its effects while in battle, or use an extremely rare medicinal item. Luckily, it is negated by the fact that Attract doesn't work on genderless Pokémon, Pokémon with the Obliviousability, or Pokémon of the same gender as its opponent.
Roost. A Flying-type move introduced in Gen IV. It became especially annoying in Black 2/White 2 where Tranquill just adores spamming it to no end. What would normally be a quick and easy battle turns frustratingly long since Tranquill will constantly use it whenever its HP starts running low.
It becomes an even more annoying move to deal with whenever Tranquill decides to use both it and Detect. Good luck dealing with a Pokémon that loves to both render your attacks useless and constantly replenishes its HP as well.
In Pokémon XD: Gale of Darkness, if you aren't using Shadow Pokémon against Ardos...."Snorlax used Shadow End!" It's the shadow equivalent of Double-Edge, and since Shadow is super effective against everything else, anything that's non-shadow will take a lot of damage. Also there's Shadow Sky. It's the shadow version of weather and pummels everyone for five turns.
Body Slam. It packs a punch and has a whopping 30% chance to cause paralysis. Paralysis is annoying because it reduces you to a crawl on top of having a 33% chance of not being able to attack. On top of that, a ton of mons could learn it in the first generation, and there it was the equivalent of Stealth Rock- hard to deal with and very widespread.
Memento, especially so in the Mystery Dungeon series. It gives a nasty offensive debuff but at the cost of the user fainting... except it's worse in Pokemon Mystery Dungeon, where everyone in the room gets this debuff, and the user simply teleports away (with only 1 HP), instead of fainting, free to use it again.
"Red's Snorlax used Rest! Snorlax went to sleep and regained health! And then, "Snorlax used Snore!"
Talonflame's Hidden Ability, Gale Wings, increases the priority of all Flying-type attacks. It also learns Brave Bird, the second strongest Flying-type attack in the game (losing only to Sky Attack, that requires a turn to charge). This translates into a 180-base power Flying-type attack that is almost always guaranteed to go first. It can wipe out entire teams if the opponent is not prepared, especially when equipped with Choice Band.
Acrobatics is a very widespread 55-base power Flying-type move that doubles in power if the user isn't holding anything. And if that user is a Flying-type, it gets a STAB as well, resulting in a move with an effective 165 base power! Very few Trainer battles have their Pokémon holding items, meaning many, many birds can hit you with a doubled Acrobatics. It's also very accurate and has a ton of PP.
Dragon Dance boosts the user's Attack and Speed. If used by the right Pokemon, it can set them up to sweep entire parties.
Any sleep inducing move, especially in Gen I when waking up used up an entire turn. Cue your enemy putting you right back to sleep. Doubly so if the user is a Psychic or Ghost-type. note Nearly all Psychic and Ghost-types learn the immensely powerful Dream Eater, which also heals the user but requires the opponent to be asleep.
Outrage was this to the point that people think the Fairy-type existed to check it. As a Dragon-type move, it had great coverage and some very powerful users, and a base power of 120 - an absurdly good number. The only downside was that it locked the user into the move for a few turns, then confused them, but you could just switch them out and then put them back in whenever needed - and as mentioned, Outrage's coverage was so good that there was never any reason not to use it; even against Steel-types, it still usually hit hard enough to punch through type advantage. Add in the common mixing of Outrage with a Choice Band or Choice Scarf (locks the user into a move, but drastically increases attack/speed) and you had what competitive players called "buttoning": simply sending in Salamence/Dragonite/Garchomp/Haxorus, selecting Outrage once, and then watching your grotesquely overpowered dragon rip the opponent's team apart, with no strategy beyond hammering the attack button. Its overuse has dropped considerably since the arrival of the Fairy-type; a level 100 Salamence in mid-button is now utterly incapable of harming a newborn Cleffa.
Agility in Pokémon Mystery Dungeon, especially in Monster Houses. Doubles the speed of every enemy in the room (they all get to go twice per turn), giving them more than enough time to wreck your party without you being able to counterattack. Even worse, the user of Agility is also granted a second turn, letting them 'use Agility again'. And if it's used twice? Quadruple speed.
Moves that hit all opposing Pokémon, like Discharge. Wonderful when you're using it, ungodly painful when fighting against it, and an enemy manages to hit you with 3 or 4 of them before coming into range. The worst variation is easily Silver Wind (used by Venomoth/Dustox/etc) and Ominous Wind (used by Drifblim for example), which not only hits you from all the way across the room, but also has a chance of raising all the opponent's stats, INCLUDING SPEED. Getting through dungeons filled with Silver Wind or Ominous Wind users turns into a Luck-Based Mission.
The Grudge Trap is That One Trap. Trip it, and every Pokemon on the floor is warped to where you are and given the Grudge status. In other words, when they go down, it drains the PP of the move you used to finish them to 0. Unless you have Warp Orbs/Seeds or Max Elixirs, you will die very quickly.
Dragon Rage early on in Pokémon Conquest. Like in the main series, when it hits it does 40 damage, regardless of enemy type or relative strength. It becomes a bit less of a hassle in long campaigns when your Pokémon generally become able to take two or three hits from it, but it's a total Game Breaker before then.
Scald. Not only is it an extremely widespread move (obtainable on most Water-types that aren't part Ice) with acceptable power, but it has an annoyingly high chance to burn, which cripples physical attackers.
Knock Off got a major buff in Generation VI. Before, it was a wimpy attack with 20 base power that just nullified the item of what it was used against. Afterwards, it not only got a decent power boost (to 65), but also inflicted 50% more damage against anything that has an item. In the competitive scheme, everybody has an item. Furthermore, you can't use your Steel-types to tank it, as they lost their resistance against Dark moves. It quickly got a reputation as "Gen VI's Scald".
Dark Void. It's a move that puts all opposing Pokémon to sleep if it connects. This means that it can completely incapaticate the enemy team in Doubles and possibly Triples. It's especially nasty when considering who can use it: Darkrai. Darkrai is incredibly fast, and most players will use Dark Void to put you to sleep before you move. However, Darkrai has an ability that causes damage to Pokémon that are asleep. This one move is what makes Darkrai such a major threat. Smeargle, who can use nearly any move in the game, can also learn this move. If you get hit by Dark Void from Smeargle, prepare to be helpless as Smeargle buffs up its stats and Baton Pass those buffs to let an ally demolish your team.
Psyshock. It's a special attack, but it targets the opponent's Defense rather than Special Defense. Add this to the moveset of a good special attacker to allow them to hit hard against a much wider range of opponents.
Bullet Punch, if used by Scizor that has Technician. Include the STAB as well and Scizor has a priority move with a base power of 90 instead of 40 and a ton of PP.
Machamp with No Guard used Dynamic Punch! Your Pokemon became confused!
Superpower when used by Malamar with Contrary. It hits extremely hard and, thanks to Contrary, increases Malamar's Attack and Defense!
Any move that puts your Pokemon to sleep, especially Spore and, to a lesser extent, Yawn, because of their perfect accuracy. Unless your Pokemon knows Snore or Sleep Talk, they will be completely defenseless.
Focus Punch, assuming you can make sure your opponent won't hit you before the attack is complete.
Breloom used Spore! The opponent's Pokemon fell asleep! Breloom used Focus Punch!
Reflect and Light Screen. They halve damage from opponents' physical and special attacks, respectively, and, while they are not permanent, they won't fade just because you switch Pokemon. If used by a Pokemon holding Light Clay, they last even longer. Setting up both of these moves is called dual-screening.
Lucian's Mr. Mime used Reflect! Lucian's Mr. Mime used Light Screen!
Using Brick Break cancels out your opponent's Reflect and Light Screen.
Trick Room. You've got a really powerful Pokemon. It can take hits really well and dish out huge amounts of damage in return. Their main weakness? They're pretty slow. But Trick Room takes care of that problem by enabling the slowest Pokemon on the field to always attack first (though higher-priority moves will still always go first), turning your Mighty Glacier into a straight-up Lightning Bruiser. Entire teams have been created to center around this move.
The foe's Aegislash used King's Shield! Now it's protecting itself from all direct attacks, and if you use a contact move on it, your Attack is reduced by two stages. Without any boosts, your Attack is cut in half. In addition, Aegislash using King's Shield also means it can switch into Shield Forme, which has massive defenses.