Hearthpwn

Populated with poisonous minions, destroy cards, and board removal, this deck is intended to defeat Lord Marrowgar by attrition. Eventually you'll have board control and deal enough damage to him so that he fatigues before you do, thus losing 30 health after the start of his turn.

Use the poisonous minions to kill off the 0|8 Bone Spikes as, like all adventure bosses, Marrowgar will often go face and leave your poisonous guys alone.

My first attempt worked; I found Despicable Dreadlord, Acidic Swamp Ooze and Shadowflame particularly helpful. Malchezaar helps by giving you extra powerful minions for asserting control over the board.

Play Kazakus for a 10-cost spell ASAP and use your hero power efficiently; you have Reno to boost you back to full health, but make sure Marrowgar always has fewer cards left in his deck than you for the fatigue win.

Elise Starseeker and Yogg provide extra backup if necessary.