Also, Veddix, I guess it's: Try to play the entire game only relying on one action but if you want to battle some bosses, (like Kurt Zisa or Sephiroth) you're going to have to use other actions and that's allowed.
Let's see........
KH2: Using the WEAKEST Keyblade in current possession. (Beginning, Kingdom Key, then the Hidden Dragon, then Sweet Memories as you obtain it.)
OH! IN all games, using NO ABILITIES, ALL UNEQUIPPED, NONE ACTIVATED. That's pretty much the 'No Sleights' rule already though for CoM.........
(Also, all CoM rules for Re: CoM)
That's all I can remember right now..... I think their were a couple others but I can't remember right now....
Oh, if you want to get really tricky, avoid as MANY Heartless battles as possible, that way when you get to the ones where you have to fight, and you can't simply move to a new area, you're really weak and have to use super skills.