Mulligans
General Mulligans
Only mulligan for Grave Defiler if you already have fiendish circle or seeds of destruction. If you do have grave defiler and a fel spell, use the defiler instead of quest on 1.
Combos: Grave defiler on 1-> Vile Library on 2 -> Fiendish Circle on 3 -> Flustered librarian and the other fiendish circle (if you need it) on 4.
Combo Mulligans
Against a combo deck all you want to do is draw through your deck and complete your quest as fast as possible while not overdrawing Neeru or Denatherius. If you end up having Wicked Shipment with Imp-ending catastrophe then do NOT trade because it will still give 3 cards on turn 3.
The goal of the deck is to make a bunch imps and beat down your opponent. To do so we have multiple board refills and an end-game strategy with Demon Seed, Neeru, and Dreadlich Tamsin.