Smash doesn't really have a debuff-focused character yet (aside from sorta Inkling), so maybe that could be his gimmick. Maybe give him Toxic, where you have to keep using the move to extend its duration and its damage goes up based on how long you can keep it active. And maybe Eerie Impulse to reduce the amount of knockback the target does. Or taunt to seal the last B move the enemy uses for a few seconds.