Hearthpwn

Magic Mirror draws lots of cards :) That's cool, because he'll fatique (easily).

You need to make sure he'll copy Tentacle of N'Zoth, Explosive Sheep or Unstable Ghoul with his secrets Duplicate and Mirror Entity. Use Frostbolt or Arcane Missiles to check if he's got Counterspell as a secret.

Use Polymorph to get rid of his biggest minions (above 5 attack) and use Flamestrike to get rid of his 2-4 minion (what's it's name...).

You need to heal, so use Ice Barrier and Cult Apothecary to do so.

It worked for me in a couple of tries (like 4-5 times). It's a hard boss, so take your time. You don't throw on minions in early play. Do that in turn 3-4, in the mean time you just get rid of his 1-1 copies with your hero power.

GOOD LUCK! let me know if it worked for you like it did for me :)