This is a new combo version of Questline Warlock and I think its actually quite good. Most of the time you arent able to combo and win in the same turn because the animations take too long. However, especially once you’ve completed the second step of the quest, you can OTK in a single turn.

Even if you dont win immediately or dont have enough time to play Tamsin in most matchups (especially against Discard Warlock) a full board and a full heal are usually enough to secure the game.

The combo works by destroying Flesh Horror with Sacrificial Summoner to summon Thaddius from your deck. You want Thaddius to reduce the cost of odd-cost cards, so you should need to combo on even turns (usually turn 4 or turn 6). Pay attention though that playing Finley while Thaddius is in hand can shift the cost cycle. Than you need to combo the same turn you play Finley or every two turns afterward.

Once Thaddius is down you can just start playing cards nearly all of them are reduced to zero mana. Darkglare is also helpful for enabling a turn 4 Tamsin because it gives you two mana