Due to experiments carried out by Doctor Moira O'Deorain, Reaper's cells simultaneously decay and regenerate at a hyper-accelerated rate. Even after the complete destruction of his body, Reaper has been observed to retain some kind of form as a black mist, apparently able to regain physical form at a later point. He has described living in the condition as a form of "constant agony," though it is only through O'Deorain's experiments that he can stay alive.