I'm in the air 90% of the time as Jigglypuff, so I'm usually airdodging. I can go over how to dodge every attack (of the first form) though:
-He does a swipe across the stage: air dodge a second after the swipe
-He is holding his head with his hands, jerking around, and a purple light starts to form on his head: Start moving towards him and the ground as quick as possible
-A reddish light ball forms on his head: Start floating off stage, that reddish light ball is about to come towards you and grab you, you need to float around it when it does.
-A bunch of purple-ish orbs form on his head: Move slowly around the stage, he's about to smash those onto you. When he stops moving, roll away and then the orbs will separate. Try to get away from the orbs, but if you can't, shield to absorb the incoming lasers.
-A bunch of energy balls form near the top of the stage: Jump offstage, he's about to lift the entire stage towards those energy balls. Just float around down there till he drops it back down.
Master Giant is probably the most involved of the forms, since you have to actually move out of the way of most of his attacks rather than just do an airdodge/roll, so I can understand you having trouble with him. I died on him a lot in my earlier attempts.