Unbreakable.G 30

I did this on the first Hero level in free play. Some people have suggested the Catwoman level as well.

Some tips:

• Break up objects as much as you can to replenish your hearts when you get hit.
• Joker seemed to work best for me. Button smash the heck out of :x:
• Before starting the level be sure to turn OFF all extras from the Pause menu (including Adaptive Difficulty)