Yeah I'm on critical mode; the best trick to it is loading up Riku with mega-potions; he doesn't die easily.
Also, a lot of the strategies that alpu guy uses really make the battle easier. Xemnas wasn't even the hardest though; I'd say he's a little easier than Roxas, a little harder than, say, Larxene.
That guy in the video made the mistake of knocking Roxas into the air (look real closely right before he does the attack) when he wasn't recovering from a combo finisher. That's why you gotta hold off from doing your entire combo; if he recovers in the air he does that.
XI Wiki

