I liked Re CoM a lot for the boss fights. Dark Riku mode made it was to easy though.Even Ansem got owned by it.It would be a normal fight till I went dark mode and then it was own in style till the fight was over.I would win the duels,use my slights,and just own. I had Vexen dazed and was just wailing on his back with just normal card attacks and he never recovered.I took off 3 bars of his health that way to beat him. I kept using sleights on replica Riku during the second fight with him.the one where u have to dive down on the boss over and over and time hitting triangle each time to keep it going.I kept using that to take him down