I think with the new PVP System:
Whimsicott should be A-/B+, it has a super Strong Ability: Prankstar + great Support Moves: Tailwind / Taunt / Fake Tears / Encore.
It also deals good Damage to Rain Teams/Water Pokes with: Gigadrain / Energyball.
Its also the 9th used Poke, in the Doubles Statistics, with a 15,93% Matchmaking Usage and a 51,87% Win Rate.