This is the deck I used to beat Heroic Chromaggus. It took me just a few tries to win. This deck wins off of a combo with Mana Wyrm, Sorcerer's Apprentice, and the cards he gives you. You absolutely must draw those cards if you want to win, so mulligan for them, as well as Duplicate. You want to Duplicate one or both of those cards for the win (note that he seems to prioritize killing Mana Wyrms heavily). With three Sorcerer's Apprentices out, all of the cards he gives you are free to cast, so you can easily buff up some Mana Wyrms for the win. Use Mirror Image and Annoy-o-Tron to shield your minions while you go for his face. You could add a Frost Nova for even more stall power.