Whimsicott

Whimsicott's Prankster, along with the combination of Leech Seed, Substitute, and Protect, allows it to outstall most non-Grass or Magic Bounce offensive Pokemon as long as it can survive one attack, regardless of if they naturally outspeed it. This can be useful against Pokemon like non-Encore Mega Lopunny and Zeraora. Whimsicott can also take on Fire- and Steel-types like Mega Charizard X and Mega Metagross when running Occa Berry or Babiri Berry, as this allows it to take a super effective attack that would usually OHKO it and affect them with Leech Seed. Thanks to its Fairy typing, Whimsicott can take on Kommo-o and Mega Gyarados with Moonblast, letting it defeat Pokemon that could otherwise beat it thanks to access to Taunt, strong attacking moves, or a natural Dark typing. Dark-types that can shrug off Moonblast damage such as Incineroar are a problem for Whimsicott, as their immunity to Prankster prevents Whimsicott from being able to SubSeed stall them. Whimsicott also suffers against sound move users like Porygon-Z and Meloetta, because both Uproar and Hyper Voice go through Substitute. Whimsicott also cannot do anything to opposing Grass-types like Mega Venusaur and Ferrothorn, as they are immune to Leech Seed and can easily take care of it with their STAB attacks.