Hearthpwn

KT and Deathrattle-taunt no longer breaks a boss. I was able to beat the boss without either. Secrets seem to "break" the lethal counter so watch out for that (The boss will attack your minions). This seems to be an attempt to play around Ice Block. In short: Secrets bad unless played before AA is out.

You can probably figure this out on your own: Survive and keep drawing cards. Spend all your mana when you can. 

• Mulligan: You want low-cost draw and Animated Armor
• Early game: Play your low cost draws.
• Mid Game: Most important part. If you don't have AA yet, keep digging and stalling. If you have it you want try to give Slither "lethal", but w/o losing too much health or using too many cards. Cone of Cold and Mirror Images shine here. Play  Frost Nova + Doomsayer if you need to.
• Late Game: beat the boss down with minions and finish them off with burn. Watch out for double Slithering Archer to clear your AA. Freeze if you have it and don't heal more than you need to (about 15 is safe as you are taking 7+ a turn),

• It's important to make sure the boss will have "lethal" next turn. Otherwise your AA may be destroyed.
• Secrets are bad, for the most part. Use them if you can figure out how. Just realize the boss will likely attack any minions.
• Icehowl will, obviously, always attack an enemy minion and it seems the boss realizes AA is trouble.   
• Boss cards (full deck):
  • 3x Slithering Archer 
  • 2x Looming Presence 
  • 3x Slithering Guard

Included

• Coldlight Oracle: Your opponent will usually already have about 8 cards in hand due to Battle Rage and Looming Presence. Pretty Much just a Arcane Int.
• Saboteur Can't find much else to put here. I tried Brann, but if you heal TOO much your minions get killed
• Polymorph for Slithering Guard and other big minions if needed.
• Doomsayer seems bad most of the time. You don't want it early, because you want cycle. It helps "buy" turns with Frost Nova and resets the board to make Mirror Image even better. 

Not Included 

• Ice Barrier: See Secrets Note.
• Duplicate: You hope  to get mirror images (?) This just stalls more and allows the boss to fill up the board. I tried it with Doomsayer and it was just too slow (double doomsayer on a board that can't deal with it) unless you also have Frost Nova. Other cards do more
• Ice Block: Curse of Rafaam is just too good. I'm serious. Also gets worse because of the way the boss interacts with secrets. Could be good if you have guaranteed lethal next turn with burn and have no freeze left. Just hope there are no curses.   
• Silence (Ironbeak Owl, Spellbreaker): No time! Maybe good for the Slithering Guard just to break the taunt.  

Secrets work early game, but get bad in the late game. This is because I assume the boss "thinks" the secret is Ice Block and attacks all your minions (this is probably wrong, but idk). 

• Lack of Large minions
  
  • Getting through the 3x Slithering Guards
  • You need to deal 57 damage If both Looming Presences are played.

• Ice Block As mentioned in the "Card Choices" section, if you want to play a "old school" freeze mage go ahead. Just hope to get the curses out of the way soon.   
• Some sort of Spell Damage: I need it to be relatively cheap and not within range of one Slithering Archer, so Kobold Geomancer, Mini-Mage, and Evolved Kobold are out. This leaves Ancient Mage, Dalaran Aspirant, [Azure Drake], and Frigid Snobold. Aspirant seems the most promising and Drake the most reasonable, but both may be too slow.
• Emperor Thaurissan and Alexstrasza: If you hit Alex and a frost nova, and have survive with enough health, you're (probably) golden.