I don’t think this card will find much use currently .
Warlock already end game with rivendare ; Sargeras seems too slow to be used without mana cheat, so he really feels like a winmore card, if you have thaddius on board you can drop him along knight , Dar’khan, flesh Behemoth. It ll give additional pressure but will it really make the deck that much better? I don’t think so, its a dead card without the thaddius hight roll .
I think it ll replace a flesh behemot in the deck, and occasionally win a game, raising the winrate a bit, but I don’t think it ll make warlock that good, what warlock need is good survival tools for the first five turn.