Pichu and Roy have noticeable differences in their movesets to make them stand out compared to Pikachu and Marth.
Denser and Wackier: In edition to being generally overpowered, characters are sometimes modified to be just outright weird, such as Fox's Landmaster being replaced by Master Hand.
Defiant to the End: If you Star KO Falco, he will trash-talk you as he's sailing off into the background.
Every character has fast moves, good hitboxes, reliable combos, and effective killing strategies.
Crazy Enough to Work: While the decision to make everyone way too powerful is questionable, it does do a pretty good job of balancing.
Competitive Balance: Granted, in a psychotic way, but most characters have reliable zero to death combos that it kinda works.
He uses dance moves, can swim in midair, can serve people like tennis balls, and one of his strongest moves is screaming " WAA".