Clarissa's Whimsicott

Clarissa's Whimsicott is a Pokémon she obtained in Unova.

As a Wild Pokémon
Whimsicott was obtained by Clarissa as a Cottonee in the Pinwheel Forest. Cottonee assisted Clarissa and her friends in getting out of the forest and finding Team Plasma. Clarissa then asked if Cottonee would like to join her, which it happily accepted.

With Clarissa
Cottonee was one of Clarissa's first Pokemon used in her battle with Burgh. Despite the type advantage that his Whirlipede had, Clarissa used her Sunstone on Cottonee which evolved into Whimsicott. With it's new evolution, Whimsicott learned Psychic and Dazzling Gleam which helped it beat Whirlipede.

Personality
Whimsicott is a polite Pokemon who shows compassion to any Pokemon and humans. This was shown when it helped Clarissa and her friends out of the Pinwheel Forest and defeat Team Plasma to get back the skull.