When on a trip in space, he and his wife were bombarded with some kind of cosmic energy. Ever since, every night, they would change. Mark, to a hulking monster whose able to control gravity. He killed many people, with his wife.
They were kept contained by S.T.A.R.-labs personnel, during the transformations. They tried to find a cure. But Joker decided to be a jerk for a change, and infected them with enough Joker venom to make them slightly more insane. Then he set them free, to kill Harley Quinn.
When they tried to do this, Harley infected them with her own blood, that has an antidote against Joker venom.
The results...not good. Instead of turning to a monster at night, Mark now turned to monster at day. And because his wife does the opposite, Moonrock can`t be with the woman he loves. Lady Luna. Who is Mark Lipkas wives evil half. They vow revenge against Harley Quinn.