This encounter isn’t hard at all, in fact it is rather easy. Basically his deck is full of legendary minions, which makes it more of a joke than an actual challenge. This means that most of the times all he gets to do is summon 1/1 taunts every turn, which should be easy to beat. You can probably take your favorite deck and stomp him with next to no trouble, although faster decks are clearly favored here. The Fast Rogue we covered a few weeks back should probably work wonders here.
Personally I used a budget Mech Mage list I had made to complete my Mage quests.
Heroic is where it gets interesting. High Justice starts the game with 3 mana rather than the usual zero. Everyone hates Ramp Druids with mad Wild Growth skill, but this guy is in another level altogether.
His constant summoning of 1/1’s make him a prime target for Mind Control Tech, though in my experience you always steal that damned Lorewalker Cho that he plays. There is a Deathwing on the opponents deck, so it might be a good strategy to try to survive until he drops it and loses his hand.
Doomsayer shines bright on this encounter as it can possibly clear a board full of high value legendaries, the AI might even choose to ignore it. Lightbomb is another powerful tool to make sure that you stay alive, so probably our best bet lies in a modified version of either Lightbomb Priest or Freeze Mage.
This will be updated later with a full deck list.
EDIT: Eldorian beat this with a Freeze Mage. Deck list and video can be found here