Quest Deathrattle Warlock

Fun fun fun!

Who doesn't like to summon giant stuff for free or... pretty cheap?

Mulligan:

The Dark Portal + early removal. Dark Portal always gives you lots of stats earlier than you should have them.

Gameplan: Try to get an early The Dark Portal to stay on board, use Plot twist to progress the quest and get some heal with Aranasi Broodmother, but try to keep one for a turn 10 Fel Lord Betrug.... if you didn't draw him from The Dark Portal anyways.
But don't be greedy! If you have a shitty hand and can exchange 6+ cards with plot twist to maybe find a solution for the board, do it! Worst case is it helps with the quest and nothing else.