Mewtwo will f*** y'alls up.
Scyther's the bug-type ninja king.
Squirtle was my first Pokémon. He's always got a place with me. Well... in spirit. I traded him to my Silver version and the battery ended up dying a few years later.
Pikachu is undeniably the face of the series and has been known to throw down. Plus in the right hands he can rape in Brawl.
However, nothing stops MissingNo.