I finished The grid with Sora and Riku (Proud mode) and I haven't died, not even once.
Zero Graviga it's an awesome command. With Sora I always do the following: as soon as the nightmares appears I put them into zero gravity and then I use Salvation or Balloonga. And tadá. For Riku I use Zero Graviaga + Balloonga (I haven't find a good 'kill 'em all' command for riku). Don't understimate the power of Zero Graviga.
As for the Dream Eaters, Kab Kannon + R&R Seal + Frootz Cat; although I have leaf bracer and second chance. R&R Seal gives you HP boost, Frootz Cat gives you magic and atack boost, kab kannon gives you defense.
For training DE just buy a lot of Balloons (+ 40 to 60 <3 when you play) and Water Barrel (+40 to 60 LP). It's important that you bond with your dream eaters, use balloons for that.
I speak spanish c:
edit: I almost forgot, when you fight prince frog use Zero Graviga that will cause the frogs to float in the air but the boss will remain on the floor c: