I was initially going to say that giving him the
Phyrexian Obliterator text and ignore the life loss possibility would've made this a lot more playable. But then I remembered that madness makes it a lot easier to flash this demon in, which could be problematic in a casual game. Nobody wants to suffer annihilator 4 on turn five. So all in all, decent card, although I think reducing both the normal cost and the madness cost by {1} wouldn't have hurt the format.
Additionally, take that
Blasphemous Act!