Hearthpwn

So... after 7 hours of not being able to complete this boss (while not looking at any other people's decklists, I tried Mill Rogue, Priest Mass Dispel (Yes, I tried this deck on my own Control Variation inclusive of Deathwing to try to do a final push and still failed the RNG by being 2 turns slower than the Heroic Boss got him down to at best 17 HP),, Priest's Reliance for Deathlords Divine Spirit Inner Fire Combo, Druid with Poison Seeds Starfall, Semi Control Warrior, Patron Warrior...etc), I finally went to my "Turn5 Faceless Mal'Ganis Dream" setup-ISH (http://www.hearthpwn.com/decks/189547-identless-malganis-lock-2), the keyword is ISH because you need more strategic cards to control the ABSOLUTE CHAOS.

The above deck link is not exactly that, but close to that in order to achieve the Mid-Game Double Mal'Ganis dream, from Voidcaller either being Shadowflame'd, Sacrificed or Traded away to obtain Mal'Ganis drop from the hand, and then Turn 5 Faceless, or Mid-Game Faceless-ing the Mal'Ganis. I had to look back to my VoD Playlist (https://www.youtube.com/playlist?list=PLwep5wHqRozPRHOlJYO6HpW77AFJKBi5p) to remember the Mid-Game Dream plays.

I will put up my highlight shortly. My final game I won on Turn 9 :D Before that, I made a HUGE mistake of not first killing the critically-hurt icehowl with like 4 HP remaining. 

By using the above sample not-refined decklist of "The Faceless Dream", imagine this:

Turn 3 Sense Demons (if you decide to include it)

Turn 4 play Voidcaller

Turn 5 Sacrificial Pact or Trading to Drop Mal'Ganis from your Hand and Faceless Manipulator to copy that Mal'Ganis.

Turn 6: Using an Ironbeak Owl or Spellbreaker to Silence an opponent's Sludge Belcher or Sunwalker or Fen Creeper.

I've had some super low-rankings but Turn6 Double Mal'Ganis dream games. So I thought that a strategy like that can be done. My humble advice is to treat this fight as-if you were doing Temple Escape or Mine Cart.

Deck Tips:

#1 Mind Control Tech are used to relinquish semi-board control "as soon as possible" or on a Crucial Turn where you Topdeck the second one, or that you have Mana to do more plays to avoid more damage taken.

#2 Ironbeak Owls are used to silence Mid or Ultra-Late Game those repetitive +1/+1 spawns that increments every turn.

In the following refining highlight, I added having Armored Warhorse: They are reasonable 4-drops to gamble jousts... and since they are 5-damage creatures, it's still pretty good for Mid-Game Shadowflame -ing... or act as decoys or that you can use as trade value.

Refining the decklist for better success:  

 The mistake of not trading into critically-hurt Icehowl cost me an earlier win (highlight soon): 

The final attempt Turn9 Win (7 mins 13 secs):