He is a shade of darkened rouge which covers his entire body. His eyes are lighted up with yellow emitting from the eyeballs. He has a patch of black hair next to his two horns. He also has a tail.
Catsby speaks far more than Twisp does, creating a sort of Jay and Silent Bob effect - albeit a far more intellectual and less vulgar one. He often speaks on non sequitur. He cares for his friend and tends to be with him at all times.
They once had tea with the moon.