I've only beat in once and that was with jigglypuff in a time of about 3:15. I would use rest on Giga Bowser and take him out really fast but then for mewtwo and Ganondorf I couldn't land rest very consistantly with them so I just ran away until I found a good item to throw at them. Another things you can do is get as far away from them as possible and then charge a rollout attack, although I recomend doing this when theres only one opponent left if at all because one time I used it fully charged on Ganondorf and he dodged it and I came back around but he dodged again and I went flying off the edge -_-