If you have a good competitive moveset for Whimsicott, post an answer below and upvote the best ones. Movesets for its pre-evolutions, if any, can also be shared on this thread.
Be sure to include full set details in your post, e.g. items, abilities, natures and EVs. Some detail, including the intended game mode for your set, is also appreciated. Access the full list of guidelines here.
Whimsicott Pokédex and learnset for reference.
Doubles Ubers / VGC 2021
Whimsicott @ Focus Sash Ability: Prankster EVs: 252 HP / 4 SpD / 252 Spe Timid Nature IVs: 0 Atk - Tailwind - Taunt - Encore - Beat Up
Ok, before you ask "why Beat Up?", I'll explain that first. What you want to do is pair this with a Pokémon with the ability Justified, preferably Terrakion, then use beat up on that Pokémon. In Doubles Ubers, this will boost their attack six stages, whereas in VGC, it'll boost their attack four stages. Keep in mind that you can Dynamax in these formats, so Whimsicott can potentially allow the Justified Pokémon to snowball through teams if they don't cycle Intimidates. Onto the other moves. Tailwind doubles your teams speed. Taunt is to shut down an opponent's attempts at setting Trick Room, and prevents them from using Protect, leaving them more vulnerable. Encore can be used on a Pokémon that successfully set up Trick Room to immediately reverse it. Max EVs in speed and Timid nature so you can outspeed and taunt Tornadus-I and potentially speed tie other Whimsicott depending on their EVs. The Timid nature and 0 Attack IVs also help minimize the damage Beat Up does to your Justified Pokémon.
Whimsicott @ Leftovers Ability: Chlorophyll EVs: 198 HP / 252 SpA / 60 Spe Modest Nature - Growth - Solar Beam - Psychic - Hidden Power [Fire]
Growth Boosts your S.Attack(and Attack but that is not important here) by two stages in the sun. Solar-beam is very Strong STAB. Psychic is for coverage. HP(Fire) is for coverage and is boosted by the sun.
Gen 8 OU
The Prank-star This name was inspired by a user named Prankstar.
Whimsicott @ Sticky Barb Ability: Prankster EVs: 4 HP / 252 Def / 252 SpD Impish Nature - Leech Seed - Switcheroo - Toxic - Substitute
Leech Seed to regain some bit of HP, as long as the user doesn't have the ability Magic Bounce or is a Dark type and also Grass type. Switcheroo to switch your sticky Barb with the opponent's so you don't have to worry about Toxic not effecting steel types. Toxic for non-Steel types and Poison-types. Substitute to protect yourself, or you could use protect instead, that way you won't have to lose any of your HP, but will have a chance to fail after using it on the first turn. A good teammate for Whimsicott might be Grimmsnarl in order to set up Light screen and Reflect to weaken the foes's attack for the team. Spirit break for Grimmsnarl to weaken any of the foes's special attack or get rid of Dark types that are immune to Prankster. Taunt to those who will try to status Whimsicott. Otherwise, hope you use this moveset :).
Here is the Pokepaste of my ideal teammate with Whimsicott
Gen 8 PU Whimsicott @ Leftovers Ability: Prankster EVs: 248 HP / 252 Def / 8 SpA Bold Nature IVs: 0 Atk - Substitute - Giga Drain / Moonblast / Psychic - Leech Seed - Encore
Basically, if you send out Whimiscott against a Pokemon who used a setup move (that's not a dark type) , you use Encore to lock the opponent into that setup move. Substitute is to help avoid you taking hits. Leech Seed is to slowly drain away the opponent's HP, and you have Leftovers to heal the Substitute recoil. Giga Drain, Moonblast, or Psychic are there so Whimsicott can do chip damage to your opponent, depending on what your team needs.
Gen 8 SS Monotype / National Dex Monotype (Grass) Whimsicott @ Pixie Plate Ability: Prankster EVs: 48 HP / 252 SpA / 208 Spe or 4 HP / 252 SpA / 252 Spe Timid Nature - Moonblast - Encore - Knock Off - Stun Spore / U-Turn
This is an Offensive(?) Utility set that Whimsicott uses on Grass-type teams in SS Monotype and National Dex Monotype. Moonblast lets Whimsicott nail Dark- and Dragon-types which helps with the Dragon matchup. Encore is used to lock setup sweepers such as Volcarona and Tornadus-T into their stat raising move, as well as opposing Pokemon into moves that work in Whimsicott's favor. Knock Off cripples most Pokemon switching in by removing their items. Stun Spore lets you slow down faster Pokemon such as Choice Scarf Pokemon, Pokemon who gained a speed boost, and naturally fast Pokemon such as Tornadus-T, Spectrier (in SS Monotype) and Cinderace. U-Turn can be used instead to bring in a teammate while doing chip damage to opposing Pokemon.
Pixie Plate is used as the item to boost the power of Whimsicott's Moonblast. 208 Speed is used to be able to outspeed non Choice Scarf Gengar, Alolan Raichu when Electric Terrain isn't up, and the Lati twins. The EV spread of 4 HP / 252 SpA / 252 Spe works as well if you prefer to make Whimsicott as fast as possible. Stun Spore is used more often in SS Monotype, while U-Turn is used more often in National Dex Monotype.
Whimsicott (F) @ Focus Sash Ability: Prankster EVs: 252 HP / 128 Def / 128 SpD Calm Nature - Taunt - Leech Seed - Substitute - Protect
You've likely faced this little guy. As such, you know what these moves are for.
Whimsicott @ Leftovers Ability: Prankster EVs: 252 HP / 252 SpD / 4 Spe Calm Nature - Substitute - Leech Seed - Cotton Guard - Giga Drain / Hidden Power [Rock] / Toxic
So what I do is send Whimsicott against a Physical Attacker and use Cotton Guard twice so his defense will be really high and he'll be able to take many hits. Next, I use Substitute and then Leech Seed so he'll get Leftovers and Leech Seed which is awesome. For the last move there are a few options Giga Drain for STAB and health regeneration with Leftovers and Leech Seed which is super duper or HP Rock for coverage and last but not least Toxic to slowly but painfully kill your opponent with Leech Seed. I like using Giga Drain just in case I get Taunted but the other moves work well too.
Role: Staller Whimsicott @ Leftovers Ability: Prankster EVs: 4 HP / 252 Def / 252 SpD Calm Nature - Substitute - Toxic - Taunt - Protect / Giga Drain / Psychic
if you are worried about being taunted use Giga Drain or Psychic.
Whimsicott @ Flame Orb Ability: Prankster EVs: 4 HP / 252 Def / 252 Spe Bold Nature - Taunt - Switcheroo - Cotton Guard - Charm / Giga Drain
Impenetrable Physical Wall. Switcheroo burns, while Cotton Guard raises Def to the max in 2 turns, while taunt destroys other taunters when they switch in. Charm is to lower Atk even further, or Giga Drain provides a way of healing, and makes you not a total taunt bait.
Whimsicott @ Focus Sash Ability: Prankster EVs: 252 HP / 4 Def / 252 Spe Timid / Jolly Nature - Taunt - Stun Spore - Encore - Memento
This is a great Pokemon to use to set the stage for a Stat booster or a Pokemon that makes use of Subs. Taunt prevents the foe from setting up any hazards or statuses that could potentially foil the strategy. Stun-spore is great for crippling and it works on all types. Encore one of the most annoying moves in the universe. And finally Memento you half the offense of the opponent then go to a Pokemon that can boost while your foe is busy swearing about his now nearly useless Pokemon. While normally after you use Memento the opponent will switch out but remember you still get in a boost on the turn they switch and they have a paralyzed Pokemon and did not get a chance to set up their hazards.
Whimsicott (M) @ Leftovers Ability: Prankster EVs: 252 HP / 252 SpD / 4 Spe Calm Nature - Cotton Guard - Leech Seed - Toxic - Protect
Taunt is a problem, but really.. it's predictable enough to switch out on. Cotton Guard will pretty much always go first (prankster) so you're set for bulky defenses. Leech Seed and Toxic will slowly kill your opponent (while Leech Seed feeds you back HP) Protect stalls out Leech seed, Toxic, AND Leftovers.
I am sooo bored. Anyways that is of no relevant use here. This is my favorite set for the cotton ball.
Whimsicott @ Leftovers Ability: Prankster EVs: 128 HP / 252 Def / 128 SpD Jolly Nature - Substitute - Toxic - Tailwind - U-Turn
Only really meant for Tailwind support. But with Prankster, he does a marvelous job. His EVs allow his to take a hit whike setting up, then with Tailwind support, he is sure to U-Turn before they hit him unless they have priority. Toxic makes a fearsome pair with Prankster as well, cause if you wall the opponent, one Sub and a Toxic can turn the tables on them.
Whimsicott makes an awesome support in double battles. Double battles set:
Whimsicott @ Big Root Ability: Prankster EVs: 252 HP / 126 Def / 126 SpD Calm Nature - Substitute - Leech Seed - Light Screen - Charm / Toxic / Tailwind
Single battles set:
Whimsicott @ Big Root / Leftovers Ability: Prankster EVs: 252 HP / 126 Def / 126 SpD Calm Nature - Substitute - Leech Seed - Taunt / Encore - Toxic / Giga Drain
Whimsicott @ Lagging Tail Ability: Prankster EVs: 252 HP / 252 Def / 4 Spe Impish Nature - Switcheroo - Encore - U-Turn / Endeavor - Taunt / Endeavor
Switcheroo can be used to permanently cripple mon's that don't have fling or switcheroo themselves. Encore is to come in and stop setup sweepers from setting up, and works well with taunt. Speaking of taunt, Whimsicott can completely shut down the likes of Sableye in particular, as it outspeeds and takes minimal damage from foul play thanks to the new fairy typing. If Taunt isn't your thing, or you already have a Pokemon with taunt, then endeavor is a cool option to do respectable damage when your health is low. U-Turn allows you to scout and provides momentum, however you can swap it out for endeavor if you prefer.
Whimsicott
This set is primarily to pick off weak and or just status opposing pokes, It does amazing if you have a slow sweeper so you may status to threats on the opposing team.
Whimsicott @ Leftovers Ability: Prankster EVs: 252 HP / 252 Spe Bold Nature - Substitute - Stun Spore - Leech Seed - Moonblast
Most likely you're gonna wanna lead off with the stun spore, then go ahead and use the leech seed to get your health back, whimsicott is an excellent sweep breaker for sure, but not so great as a lead considering most people lead off with the biggest threats at the beginning of the battle, once those are gone, he's clear for take off.
Whimsicott @ Leftovers Ability: Prankster EVs: 252 Def / 128 SpA / 128 SpD Careful Nature - Double Team / Substitute - Giga Drain - Leech Seed - Cotton Guard
I was so annoyed by this thing once and since then I've carried an always hitting move on EVERY team. The next time it came it was dead. I had a feeling that it was kinda popular and I wuz right. lol so annoying.
Tried out this trolly set, fun to use:
Whimsicott @ Rocky Helmet Ability: Prankster EVs: 252 HP / 252 Def / 4 SpA Bold / Calm Nature - Cotton Guard - Encore - Leech Seed - Giga Drain
Caution: Expect rage quits.
For use after the removal of poison types and maybe special sweepers. Come in on a setup mon (sweeper or defensive, doesn't matter), use encore, set up cotton guard and leech seed, and annoy your opponent.
Whimsicott (F) @ Choice Specs Ability: Infiltrator EVs: 6 Def / 252 SpA / 252 Spe Modest Nature - Energy Ball - Moonblast - Hurricane - Shadow Ball
Timid can be used instead of Modest. Anyways, not much to explain here. Energy Ball & Moonblast are STAB, while Hurricane & Shadow Ball are coverage. Infiltrator hits through Substitute & Screens.
Nothing is better than this
Whimsicott (F) @ Leftovers Ability: Prankster EVs: 248 HP / 252 Def / 8 SpA Timid Nature - Attract - Leech Seed - Substitute - Grass Knot
Trust me.
Whimsicott @ Leftovers Ability: Prankster EVs: 252 HP / 4 Def / 252 SpA Quiet Nature - Leech Seed - Substitute - Protect - Nature Power