Hearthpwn

With this deck modeled after the Awaken the Makers deck, I was able to defeat Lady Deathwhisper, Blood-Queen Lana'thel, Sindragosa, and The Lich King without too much difficulty. Each time I was able to outlast the boss, either winning by fatigue and/or having multiple cards to play with him/her playing one card per turn. Archbishop Benedictus was quite helpful, giving me some of the boss's cards (usually great) that normally you wouldn't be able to play.

The good thing about deathrattle minions that upon death summon another minion is their stickiness. Since most of the time boss minions go face, that leaves your minions ample time to gradually assert control through attrition, which coupled with the multiple board-clear spells give you dominance.

Furthermore, you will have less health than the boss most of the time. Use Reno and Amara to boost you back to 30 or 40 health, Kazakus for the sheep and/or board clear, Obsidian Statue for significant health return (especially with multiple enemy minions), and of course Yogg-Saron as a backup. Elise Starseeker combined with Benedictus + Brann can even give you a whole bunch of legendaries, but I never had to/was able to do that.

Keep in mind the 2-, 3-, and 5-damage board-clear spells you have; use them well for the few times the boss has board control.