jigglypuff is probably the best to use against gigabowser, mewtwo, and ganondorf
for gigabowser, just jump to his face and use her…ugh...i forgot which skill...B up? or was it B down...
anyway, do that and you'll send him flying
3 times will be enough to knock him off the stage
(or if you're lucky he might just fall off in one hit)
but of course, you'll have to avoid mewtwo and ganondorf while you go after gigabowser, try not to get hit by them or you're done for
and after you've taken out gigabowser
I usually use the cheap charge up roll attack for mewtwo and ganondorf
but sometimes they're smart and will dodge and throw stuff at you
so just play the 'hit and run' game with them
(throwing items or using good or longranged weapons is always good)
but if you're up for a challenge, use anyone to beat them :x
I beat them with mario and falco before : D~