That's freaking dark.
Summon a sealed, super strong demon. Slaughter it yourself, to reanimate it afterwards and slaughter it again..
Is it warlock only, I don't have the set with me? If not, the necromancer could even use it to fuel his graveyard. (I think this would be borderline OP)
Hes not Warlock only, but you can only reanimate him once. After the Animate brings him back, he has a zombie marker on him, so he will be obliterated when he dies the second time.
But yeah, if a Graveyard is in play you could spend 6 to summon him, sac him on the alter and get 4 mana added to the spawnpoint while getting a +4 Melee/Pierce boost. Then get 4 mana more re-sac'ing him after Animating him. Your graveyard would get 8 mana out of the deal, and youd spend 9 between Meh and the reanimate. Not a huge gain, but itd basically be a huge damage boost that almost pays for itself int aht case.