Whimsicott
Grass
Ability: Prankster / Infiltrator / Chlorophyll
HP: 60
Attack: 67
Defense: 85
Sp.Attack: 77
Sp.Defense: 75
Speed: 116

Grass
Ability: Prankster / Infiltrator / Chlorophyll
HP: 60
Attack: 67
Defense: 85
Sp.Attack: 77
Sp.Defense: 75
Speed: 116
Cute little thing, isn't it?
Gen V Level-up Moves
Gen V TM Moves
Gen V Egg Moves
SubSeed
Whimsicott @ Leftovers
Timid
Ability: Prankster
36 Def / 252 SpD / 220 Spe
-Substitute
-Leech Seed
-Taunt / Encore
-Toxic / Protect
Whimsicott's standard set on GBU Doubles/Triples. Substitute + Leech Seed is extremely hard to get past without a strong STAB or Super-Effective attack.
Without the speed EVs given, you are always outsped by Timid Thundurus who can potentially get a Taunt in before your Substitute is up, and opposing Whimsicott who run max speed will out-do you anyway. If that isn't a concern, a much more bulky spread is 252 HP / 252 Defense / 4 SpD with a Bold nature, or alternatively 252 HP / 4 Defense / 252 SpD with a Calm nature is available.
Doubles / Triples Tailwind
Whimsicott @ Leftovers / Focus Sash / resist berry
Bold / Timid
Ability: Prankster
252 HP / 252 Def / 4 SpD
-Tailwind
-Encore
-Helping Hand
-Taunt / Stun Spore / Trick Room
Thanks to Prankster, Whimsicott is almost guaranteed to get Tailwind up. Whimsicott is also the fastest Encore user. Helping Hand is used to rediculously power up it's partner's attack. The final move is of course user preference; Taunt to shut down opposing setup Pokemon, Stun Spore to induce paralysis, and Trick Room to reverse the effects of Trick Room (which negates Tailwind).
Other Options:
Whimsicott has a plethora of utility options at it's disposal, making it slightly unpredictable for your opponent outside of just SubSeed. Should you feel the need to attack, your primary attacks should be Giga Drain or HP Fire, but if you want an attacking grass type, I recommend a different Pokemon. In a singles set it can run Cotton Guard to boost it's defenses to sky high levels, making it extremely hard to take down physically. In doubles and triples, Fake Tears is a great way for a special sweeper to net some very fast KOs.
Doubles / Triples Partners:
Since Whimsicott typically lacks offense at all, it needs partners that can attack, or help it stall. Any partner that has a strong Fire attack works great for taking down opposing grass types, and especially for taking down Ferrothorn is an asset. Whimsicott makes an excellent utility Pokemon in doubles and triples thanks to it's access to Tailwind, Encore, Helping Hand, and Worry Seed. Whimsicott works well on Rain teams, since under Rain it's weakness to Fire is negated.
Check/Counters:
Opposing Prankster users (namely Thundurus, Tornadus, and opposing Whimsicotts) can hit you with Taunt before your substitute is up, completely shutting you down; Tornadus can also hit hard with a SE Flying attack. Sets lacking Toxic are walled by grass types, and some grass are also poison types as well, rendering Toxic useless. Ferrothorn also stops you hard no matter what set you run.
Gen V Level-up Moves
PHP:
Cottonee
Start Absorb
4 Growth
8 Leech Seed
10 Stun Spore
13 Mega drain
17 Cotton Spore
19 Razor Leaf
22 PoisonPowder
26 Giga Drain
28 Charm
31 Helping Hand
35 Energy Ball
37 Cotton Guard
40 Sunny Day
44 Endeavor
46 SolarBeam
Whimsicott
Start Growth
Start Leech Seed
Start Mega Drain
Start Cotton Spore
10 Gust
28 Tailwind
46 Hurricane
Gen V TM Moves
PHP:
TM06 Toxic
TM10 Hidden Power
TM11 Sunny Day
TM12 Taunt
TM15 Hyper Beam
TM16 Light Screen
TM17 Protect
TM20 Safeguard
TM21 Frustration
TM22 SolarBeam
TM27 Return
TM29 Psychic
TM30 Shadow Ball
TM32 Double Team
TM42 Facade
TM44 Rest
TM45 Attract
TM46 Thief
TM48 Round
TM53 Energy Ball
TM56 Fling
TM68 Giga Impact
TM70 Flash
TM85 Dream Eater
TM86 Grass Knot
TM87 Swagger
TM90 Substitute
TM92 Trick Room
Gen V Egg Moves
PHP:
Beat Up
Encore
Fake Tears
GrassWhistle
Memento
Natural Gift
Tickle
Switcheroo
Worry Seed
SubSeed
Whimsicott @ Leftovers
Timid
Ability: Prankster
36 Def / 252 SpD / 220 Spe
-Substitute
-Leech Seed
-Taunt / Encore
-Toxic / Protect
Whimsicott's standard set on GBU Doubles/Triples. Substitute + Leech Seed is extremely hard to get past without a strong STAB or Super-Effective attack.
Without the speed EVs given, you are always outsped by Timid Thundurus who can potentially get a Taunt in before your Substitute is up, and opposing Whimsicott who run max speed will out-do you anyway. If that isn't a concern, a much more bulky spread is 252 HP / 252 Defense / 4 SpD with a Bold nature, or alternatively 252 HP / 4 Defense / 252 SpD with a Calm nature is available.
Doubles / Triples Tailwind
Whimsicott @ Leftovers / Focus Sash / resist berry
Bold / Timid
Ability: Prankster
252 HP / 252 Def / 4 SpD
-Tailwind
-Encore
-Helping Hand
-Taunt / Stun Spore / Trick Room
Thanks to Prankster, Whimsicott is almost guaranteed to get Tailwind up. Whimsicott is also the fastest Encore user. Helping Hand is used to rediculously power up it's partner's attack. The final move is of course user preference; Taunt to shut down opposing setup Pokemon, Stun Spore to induce paralysis, and Trick Room to reverse the effects of Trick Room (which negates Tailwind).
Other Options:
Whimsicott has a plethora of utility options at it's disposal, making it slightly unpredictable for your opponent outside of just SubSeed. Should you feel the need to attack, your primary attacks should be Giga Drain or HP Fire, but if you want an attacking grass type, I recommend a different Pokemon. In a singles set it can run Cotton Guard to boost it's defenses to sky high levels, making it extremely hard to take down physically. In doubles and triples, Fake Tears is a great way for a special sweeper to net some very fast KOs.
Doubles / Triples Partners:
Since Whimsicott typically lacks offense at all, it needs partners that can attack, or help it stall. Any partner that has a strong Fire attack works great for taking down opposing grass types, and especially for taking down Ferrothorn is an asset. Whimsicott makes an excellent utility Pokemon in doubles and triples thanks to it's access to Tailwind, Encore, Helping Hand, and Worry Seed. Whimsicott works well on Rain teams, since under Rain it's weakness to Fire is negated.
Check/Counters:
Opposing Prankster users (namely Thundurus, Tornadus, and opposing Whimsicotts) can hit you with Taunt before your substitute is up, completely shutting you down; Tornadus can also hit hard with a SE Flying attack. Sets lacking Toxic are walled by grass types, and some grass are also poison types as well, rendering Toxic useless. Ferrothorn also stops you hard no matter what set you run.