Now that he's locked up in Arkham, Gotham City is safe from the threat of Clayface. But what led Clayface to become the monster that he is? The answers lie here.
Clayface is locked up in Arkham and Mogsy, the guy in the cell next to him, is his biggest fan. Mogsy begs Clayface to recite his old roles, which Clayface is happy to do.
Soon Karlo gets spooked by Scarecrow and tells Mogsy about how he used to be too normal and no one noticed him. He tried new clothing and acting but couldn't stand out of the crowd. He goes on to tell how he made a deal with the Penguin for some magic clay. The clay turned him into Clayface, but at first everything seemed to be going Karlo's way but then Penguin came to collect his debt. He had Clayface commit crimes for him and that cost Karlo his acting career and his life spiraled downward.
When Clayface finishes his story he realizes that Mogsy has passed away. After day of being depressed, he decided to break out and fakes an injury and when the doctors come in his cell to help he makes a crack and escapes.