Randomly, Joker, in the Joker's Carnival DLC combat challenge stage, will become unhittable. He'll still move as though he is fighting, but he'll never attack, he won't be able to be targeted, and I don't think he can be hit by anything. I think it happened once after I did a beatdown finisher on him. What causes it to happen?
Update: Here's footage of it happening:
Best Answer
In Riddler's Challenges, the final level of a challenge is forcibly with 2 modifiers: time limit and random unhittability.
Maybe that DLC uses the same modifiers.