level doesn't matter. 5 surges and 3 cures, make sure you have once more and second chance. just lock on and surge/dash to move. when he catches you with hook/rope move, surge is the only way to move out of it. spam surge when he uses fire pillars, surge when he steals your commands, surge when he's invisible (he isn't invulnerable). the brief window of invincibility granted by thunder surge is your best friend and triggering the command style finisher is helpful as well. good luck.
Funnily enough, about an hour after I posted, I defeated him. Just got to do the same feat with Ven and Aqua. But going to take a break for a few weeks before heading back to 100% Ven's story.
Funny, I never once experienced a glitch in 2.5.
Neither did I. Or in 1.5.
Then you are a child blessed by luck. The Xemans battle in particular is a glitch hell.
I never had the Xemnas battle glitch either. And i've played on all difficulties. If it was a genuine glitch, wouldn't it affect everyone? Hearing about the Xemnas battle glitch made me nervous to tackle Xemnas but I just pressed triangle when it told me to and it worked every time.