Hearthpwn

This is the deck I used to beat Lord Marrowgar quite easily.

Curve out into 5 attack minions, use crazed alchemist and book wyrm to deal with the spike. Play Barnabus and then play huge dragons for cheap.

Alexstrasza can be used for a quick finisher, but you can also play her for tempo at 0 mana if you want because the board you'll generate is far too huge for him to deal with anyway.

You might overdraw if you play Ultimate Infestation with Chromaggus in play, but it's totally fine because Marrowgar himself will hit fatigue before you will.