The mulligan for this deck is quite different each game, the only sure fire cards to keep are Stone Hill Defenders, Defiles, and the Spellstones. Plated Beetle is ok to keep as well.
The others will depend on your opponent and whether you have the coin or other cards in hand.
Keep hellfire if you are against a possible aggro opponent. Paladins almost certainly.
Keep Oakheart if you have the coin and suspect a slower control opponent same with Skull of the Man'ari
Keep Vulgar Homunculus if you have a spellstone already
I just opened up Master Oakheart and it has re-vitalized my interest in Hearthstone again. I highly recommend getting it if you are sick of all the boring meta decks. I have made so many fun decks with all the different classes highlighted around this card.
The deck works similarly to any other control warlock in which case you keep tapping for many cards until you get what you need. It has less healing than say a Cubelock, but makes up for it with a lot more taunts to save you until the later game where you have 4 huge threats that you hopefully can get at least 1 off.
Threat 1 at turn 5 Skull of the Man’ari same idea as cube lock works great to pull any demons in your hand.
Threat 2 at turn 9 Master Oakheart will pull any combination of 1,2, and 3 attack minions:
1 attack minions meat wagon which in turn will pull your summoning portals to make your other minion cheap, stone hill defenders which is the worst possible scenario, try and hold these in your hand whenever possible, but it is still a nice free taunt to pull and not the end of the world, Tar Lurkers which are very annoying and great value at 5 man for free
2 attack minions plated beetle also synergizes with N’Zoth, Vulgar Homunculus synergizes with Guldan and also you won’t take damage, possible drawback as it being one of your spellstone activators, but again not the end of the world
3 attack minions Rin the Desciple or Voidlords, you can not beat the value in either case
Threat 3 at turn 10 N’Zoth
Threat 4 at turn 10 Guldan
I also added Prince Malchezar as he is an extra demon for Guldan and he can add some extra cards for some random excitement, this card could possibly be left out, but it makes the deck fun and unpredictable.
Skulking Geist was a definite add as the deck has no 1 cost spells.