Well Ansem can be realtively easy even if you have low DP. just keep attacking him and when he uses sleights, especially his dark attack thingy, quickly scroll to the back of your deck and use one of the zero cards, then reshuffle (you don't have to) and repeat the process. Stock up on mickey cards, use oogie boogie's regen card, or malificent's overdrive card. When you do go into dark mode though, look for the three nines in your deck and use Dark Aura and any other sleights until you return to normal.
hope that helps