I think people who used to play competitively should get a guide because seriously it's not that hard guys. Here you go
FightAdamantEevee
NOTE: There are spoilers of Pokémon from recent generations in here. If you prefer to check them out yourself in-game, then do that instead.
Anyway, Gen IV was three generations ago (and my first game, though I didn't play competitively at the time), so I'll give you information on the things that took place between generations.
Generation IV to Generation V
Hidden Abilities were introduced. These were given to most Pokémon except ones that were based around their ability (such as Slaking). Here are the Hidden Abilities that most influenced Pokémon in OU:
- Zapdos got access to Static, allowing it to be an annoying wall against Pokémon that spam U-Turn.
- Tangrowth and Slowbro got access to the newly introduced Regenerator, which heals one-third of a Pokémon's health when it switches.
- Salamence and Gyarados, though they didn't get it right away, got Moxie. This new ability raises the Pokémon's Attack every time it KOs an opponent and turned them into powerful Dragon Dance users.
- Garchomp got Rough Skin, but this buff didn't contribute to its eventual drop back into OU.
- Clefable got Unaware. This might not seem significant yet, but...
- Nidoking got Sheer Force, so it ran a special set using its great movepool, which contains moves like Ice Beam and Flamethrower.
- Gliscor got Poison Heal, increasing its annoyingness. By spamming Substitute and Roost, it could infinitely stall out any slower Pokémon.
- Most importantly, Ninetales and Politoed got access to Drought and Drizzle, respectively. This led to the infamous "weather wars" of the fifth generation.
Key Pokémon introduced in the fifth generation:
Keldeo, a Water/Fighting-type has impressive Speed and Special Attack. Its movepool is shallow, not even containing Ice Beam, but it can still run sets such as Choice Specs, Choice Scarf, and Substitute + Calm Mind.
Sample set:
Keldeo @ Choice Scarf
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Scald
- Secret Sword
- Hydro Pump
- Icy Wind
Volcarona, a Bug/Fire-type Pokémon, has a 4x weakness to Stealth Rock. However, it has access to the newly introduced Quiver Dance. With the right amount of support, Volcarona can easily blow through teams.
Sample set:
Volcarona @ Firium Z
Ability: Flame Body
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Fire Blast
- Hidden Power [Ground]
- Giga Drain
- Quiver Dance
Hydreigon, a Dark/Dragon-type, is the pseudo legendary of Generation V. It sits at below 100 base Speed, but it has incredible Special Attack. Many defensive teams were dismantled by Draco Meteors.
Sample set:
Hydreigon @ Choice Specs
Ability: Levitate
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Draco Meteor
- Dark Pulse
- Flash Cannon
- U-turn
Tornadus, Thundurus, and Landorus (left to right) had impressive Speed and attacking stats. Tornadus and Thundurus got access to the ability Prankster, which gave all status moves a +1 priority, but Landorus was the one that ultimately got banned. Sheer Force, along with good stats in both Attack and Special Attack, meant that Landorus could run tons of sets.
Shown here are the Therian forms of the three Pokémon. Their stats are redistributed, with all except Tornadus giving up Speed for other stats and abilities. Tornadus received Regenerator, Thundurus got Volt Absorb, and Landorus got Intimidate. This is what caused Landorus-T to become one of the most important parts of OU today: it can run both offensive and defensive sets such as Stealth Rock and Choice Scarf.
Sample set:
Landorus-Therian @ Rocky Helmet
Ability: Intimidate
EVs: 252 HP / 252 Def / 4 Spe
Impish Nature
- Stealth Rock
- Earthquake
- Knock Off
- U-turn
Ferrothorn, a Grass/Steel-type, is a tank that can take on many different Pokémon. Its role is usually setting Stealth Rock and wearing opponents down with Leech Seed and its formerly signature ability, Iron Barbs (a clone of Rough Skin). Its decent Attack stat means that even uninvested Gyro Ball and Power Whip do lots of damage.
Sample set:
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 252 Def / 4 SpD
Relaxed Nature
IVs: 0 Spe
- Power Whip
- Leech Seed
- Gyro Ball
- Stealth Rock
This is Excadrill, a Ground/Steel-type. Excadrill usually uses the ability Sand Rush, which doubles its Speed stat in a sandstorm. This, along with Swords Dance and opportunities to set it up, led to Excadrill's ban in Generation V. It's dropped down to OU in the latest generations, however. Excadrill can also run sets that utilize Rapid Spin and its Hidden Ability, Mold Breaker, in sets such as Choice Scarf and Specially Defensive.
Sample set:
Excadrill @ Life Orb
Ability: Sand Rush
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Swords Dance
- Earthquake
- Iron Head
- Rock Slide
Scolipede, a Bug/Poison-type, is used for its Speed Boost ability. Higher bulk than Ninjask in combination with an arguably better defensive typing caused Scolipede to be the face of many infamous Baton Pass teams. Even after passing Speed along with other stat boosts was banned, Scolipede still uses Swords Dance sets to sweep on its own.
Sample set:
Scolipede @ Waterium Z
Ability: Speed Boost
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Swords Dance
- Aqua Tail
- Earthquake / Megahorn
- Poison Jab
Key items introduced in the fifth generation:
- Rocky Helmet, which hurt the opponent by 16% if they hit the holder with a contact move, sees use on defensive Pokémon such as Landorus-T and Zapdos. It's used on Rough Skin/Iron Barbs Pokémon to hurt physical attackers by around 30% for each attack.
- The elemental Gems (Fire Gem, Dark Gem, etc.) provided a one-time 1.5x boost to a move. However, they were later nerfed to only 1.3x (iirc), so they don't see much use except on Flying Gem + Acrobatics sets.
- Eviolite, which gave the holder 1.5x Defense and Special Defense if its species could evolve, caused Chansey to overshadow Blissey; it didn't do much else, though.
Key moves introduced in the fifth generation:
- Quiver Dance increases the user's Special Attack, Special Defense, and Speed by one. It has low distribution, however, only being learned by certain flying Bug-type Pokémon.
- Shell Smash lowers the user's Defense and Special Defense by one, but increases their Attack, Special Attack, and Speed by two. It also has low distribution, being restricted to only certain shelled Pokémon (usually Rock-types).
- Acrobatics is a Flying-type attack that has only 55 BP, but it increases to the much stronger 110 if the user has no item. It is used both on itemless sets and on those that use a Berry or a Flying Gem.
- Secret Sword is Keldeo's signature move. It's a special Fighting-type move with 85 power, but it hits the opponent's Defense like Psystrike.
- Psyshock is a weaker version of Psystrike, but most Psychic-types can learn it through TM. Pokémon like Alakazam often use it to break through Chansey.
Generation V to Generation VI
Generation VI had two changes that really stood out: a modification to the type chart and the introduction of Mega Evolutions.
The most notable part of the type chart's modification was the introduction of the Fairy type. In addition to the many Fairy-types introduced in the sixth generation, many older Pokémon had their types changed, such as Gardevoir, Azumarill and Clefable.
Fairy is weak to Poison and Steel, and it resists Bug, Fighting, and Dark with an immunity to Dragon.
Offensively, Fairy is super effective against Fighting, Dark, and Dragon, while it is resisted by Fire, Poison, and Steel.
The only viable new Fairy-type moves in OU are attacks; the status moves are either unviable (Baby-Doll Eyes) or old moves with their types changed (Charm).
The other change to the type chart was Steel losing its resistances to Ghost and Dark. This increased the viability of Ghost as an offensive typing while encouraging the use of Knock Off.
Mega Evolutions are in-battle alternate forms that certain Pokémon can achieve. The Pokémon must hold the appropriate item to Mega Evolve; additionally, only one Pokémon per side can Mega Evolve.
Key Pokémon introduced in the sixth generation:
Mega Metagross, unlike its regular form, has as much Speed as Latios. It uses this to its advantage, too-- high base Attack, an ability that increases the power of contact moves by 4/3, and enough coverage to hit all of OU means that Metagross is one of the best Mega Evolutions. Its Steel STAB is much more valuable in a meta full of Fairy-types, too.
Sample set:
Metagross @ Metagrossite
Ability: Clear Body
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Meteor Mash
- Thunder Punch
- Ice Punch
- Bullet Punch
Mega Charizard X and Mega Charizard Y are potent threats for different reasons. While Mega Charizard X aims to set up with a Dragon Dance or two before blasting its way through teams with STAB moves boosted by Tough Claws, Mega Charizard Y breaks through teams with no need for setup: its Speed is somewhat average, but an immense Special Attack stat backed up by Drought ensures that anything hit neutrally, unless it's Chansey, will faint.
Sample sets:
Charizard @ Charizardite X
Ability: Blaze
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Dragon Dance
- Earthquake / Roost
- Dragon Claw
- Flare Blitz
Charizard @ Charizardite Y
Ability: Solar Power
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Fire Blast
- Solar Beam
- Focus Blast
- Roost
Zygarde, a Ground/Dragon-type, didn't receive much hype in the generation it was introduced. However, the introduction of its signature move Thousand Arrows means that it can run many sets, such as Substitute + Coil, Choice Band, and bulky Dragon Dance.
Sample set:
Zygarde @ Choice Band
Ability: Aura Break
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Thousand Arrows
- Extreme Speed
- Iron Tail
- Toxic
Greninja, a Water/Dark-type, has mediocre stats outside of its impressive Speed. However, it's salvaged by its abilities, Protean and Battle Bond. Protean Greninja lures in opponents and hits them hard with coverage moves, while Battle Bond sets aim to get a KO by using Choice Specs.
Sample set:
Greninja @ Choice Specs
Ability: Battle Bond
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- U-turn
- Hydro Pump
- Dark Pulse
- Water Shuriken
Mega Mawile is one of the best Mega Evolutions because of two things: an added Fairy typing and the ability Huge Power. Mawile can devastate offensive teams by setting up with Swords Dance due to incredible defensive typing, then demolishing opponents with moves such as Play Rough and Sucker Punch.
Sample set:
Mawile @ Mawilite
Ability: Intimidate
EVs: 252 HP / 252 Atk / 4 Spe
Adamant Nature
- Swords Dance
- Sucker Punch
- Thunder Punch
- Play Rough
Mega Sableye is a staple on most stall teams nowadays because of its ability, Magic Bounce, which acts as a permanent Magic Coat. Calm Mind sets were more popular during the time immediately after it was released, but utility sets, such as the one below, took their place.
Sample set:
Sableye @ Sablenite
Ability: Prankster
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Fake Out
- Knock Off
- Will-O-Wisp
- Recover
I can guarantee that you will lose to this at least once. Don't use it, though.
Key items introduced in the sixth generation:
- Assault Vest, which increases the user's Special Defense by 1.5x but only allows them to use damaging moves. It's popular on some Regenerator users such as Tangrowth.
- Mega Stones, which enable Mega Evolution.
Key moves introduced in the sixth generation:
- Thousand Arrows is a Ground-type 90 BP move that hits Flying-type and floating Pokémon neutrally and gives them the Smack Down status, effectively removing their floating effect and opening them up for hits that aren't neutral. For instance, a Zapdos will be hit neutrally by one Thousand Arrows, but super effectively by the second.
- Sticky Web is an entry hazard learned only by a specific few Bug-types. It lowers the Speed of grounded Pokémon when they switch in.
- Grassy Terrain, Electric Terrain, and Misty Terrain were introduced. Grassy Terrain increases the power of Grass-type moves by 1.5x and gave each Pokémon recovery on the level of Leftovers; Electric Terrain prevents each Pokémon from falling asleep and increases the power of Electric-type moves by 1.5x; Misty Terrain prevents each Pokémon from any status and decreases the damage they take from Dragon-type moves. (Note that terrain effects only apply to grounded Pokémon.) Due to their bad distribution, terrains weren't seen much in Generation VI.
- Play Rough is a physical Fairy-type move with 90 base power and 90% accuracy; Moonblast is a special Fairy-type move with 95 base power, 100% accuracy, and a 30% chance to lower Special Attack.
Generation VI to Generation VII
Generation VII introduced many new OU Pokémon, and it also introduced Z-Moves, which are more powerful versions of regular moves.
The Tapu Crew
(Left to right: Tapu Koko, Tapu Lele, Tapu Bulu, Tapu Fini)
Generation VII introduced Pokémon that automatically set terrains, along with a new terrain, Psychic Terrain: under Psychic Terrain, Psychic-type moves get a 1.5x boost, and Pokémon are protected from all priority moves. Teams built around terrains are uncommon because of their mediocre offensive types, but there are certain cores, such as Tapu Lele + Mega Metagross, that can really shine.
I need to get some homework done so I can't help with the other mons, but you can hopefully use the Strategy Pokédex or the OU Subforum if you need help.
If people want to put this somewhere else then I can edit in the latest generation information tomorrow (and fix the sets because some of them are probably suboptimal).
