Well, I've used Link, Fox, Mario, and Jigglypuff.
Link, make sure you use alot of long ranged attacks, and alot of spin attacks.
Fox, just be really fast, and try to keep them off their feet. Use alot of Fox Illusion, blaster, and Fire Fox. Make sure to activate the Reflector when they throw an item.
Mario, use the cape to deflect things back, use a Meteor Smash on Giga Bowser. Use everything you got.
Jigglypuff.... You know the drill.
Credit for Sig & Avy goes to Yogi_Bear