Hearthpwn

This is the hardest fight in this Adventure.  You have to defeat a to-the-face warrior who can summon 3/3 charge minions as a hero power.  When she dies, Malchezaar comes in with 10 mana, and a hero power that summons 2 6/6 infernals for 2 crystals.  And he immediately clears off your board with Twisting Nether.  

So you have to shift from fighting an aggressive deck to fighting a very potent late-game board.

This deck is designed to stall against the warrior long enough to summon a bunch of deathrattle minions who will all die to the either the warrior attacks or the Twisting Nether.  Then, you will bring them all back with N'Zoth, and hopefully use Shadowstep.  This will give you some breathing room to smash in Malchezaar.