In the duo fight where you are inside the theater and several Batman characters appear (Catwoman, Batwoman, Batgirl, Nightwing, etc) sometimes one will appear on the upper balcony in the back (was Batwoman for us). They don't attack or fight, but if you go after them, they Evade several times before you can do damage to them. When you can do damage, they still don't move but after they get down to 80% health, they reset. You have to pull or knock them off the balcony somehow before they activate. Took us almost 15 minutes to get her over the edge and finish the fight.
I posted about this in the Arkham Asylum Bug Forum. I got a reply they were going to fix it. Be sure to post in that thread too, so it catches the bug catchers' attention.
