Batman is required in all matches of challenge battle 5. It's a very easy condition to fulfill, as he has more versions than any other character. For new players, the fairly solid Batman/Prime is guaranteed from the Starter Pack.
Challenge: Life Drain! (10%)
Challenge: Radiation! (1% max health lost every second)
Challenge: Life Drain! (enemies heal by 10% of their damage dealt)
Challenge: Radiation! (2% max health lost every second)