#052 Unova / #546 National
Species classification: Cotton Puff Pokemon
Prankster – Non-damaging moves get a 1 point priority boost
Slip Through – Safeguard, Lightscreen and Reflect have no effect on user
Dream World abilities: Chlorophyll – Speed doubles during sunny weather
Black: Pinwheel Forest
White: Nacrene City (NPC woman in the duplex directly east of the Pokemon Center will trade your Petilil for her Cottonee or vice versa depending on which version of the game you have)
Wild hold items: None
Egg groups: Plant, Fairy
Capture rate: 190
Gender ratio: 50/50
Effort values: 1 Speed
Evolution family: To Whimsicott via Sun Stone
Cottonee and its evolution Whimsicott look too cute to be really useful at first glance, but they've definitely got their advantages in battle. As you know, Leech Seed is the most formidable Grass-type move in existence. Once you've seeded your opponent, Leech Seed takes 1/16 of its HP each turn, and gives all the HP it drained from your opponent to your Pokemon. 1/16 doesn't seem like much, but it adds up quickly, since once you've seeded the Pokemon, it drains HP each turn like a poison, without taking up additional turns, and you get the full amount restored to the Pokemon who used Leech Seed, or if you switch out, to whatever Pokemon takes its place. If you add a Big Root hold item to that equation, you get the full HP of your opponent plus 30%.
Cottonee and Whimsicott's Prankster ability gives priority to non-damaging moves, and Leech Seed is included in this since it doesn't do damage when the opponent is seeded initially. Add to that Whimsicott's already impressive speed stat, and it has the potential to seriously disrupt your opponent's plans. Prankster coupled with Whimsicott's speed also go hand in hand for any other non-damaging strategies you can think of, like Substitute, Encore and Taunt.