He introduced himself as an absolute jerk who brags too much. He has the power to heal people, and so Malleo needed him to heal Weegee. But he doesn't do it for free. When Weegee said he saw someone, he called him an idiot. He also defeated Fortran in a tournament, and he likes to taunt Malleo with it by bragging. Weegee challenged him to a tournament, but Kelljeller also made a deal. Basically if Weegee wins, Weegee can decide his punishment, but if he wins, Fortran has to sell himself to demons.