The only way that you can OTK someone with so much armor is if you had Antonidas + 0-mana fireball. The main counter to this, as noted by many comments in this thread is Loatheb. Now, the only way for lethal that I can think of requires very lucky RNG from Yogg. Assuming the enemy board has Mal'ganis, Sneed's (to respawn Mal'ganis) Loatheb (played on the previous turn), Mad scientist, Shredder (to respawn Scientist). The enemy also has a christmas tree of Mage secrets (counterspell and effigy are the only secrets that might stop this).

I know some of you will not find this valid because you can never dictate what Yogg does but I think it's the only way.

My combo is: Yogg-Saron -- Yogg casts: [any random spell](procs Counterspell), Twisting nether (Kills Board. Mal'ganis spawns from Sneeds, Mad Scientist gets enemy a secret, Scientist spawns from Shredder). Now effigy will trigger depending on play order. The worst case here is spawning another scientist which will give him another two secrets. Another Mal'ganis won't hurt because he already has one. Assume the secret grabbed by the first scientist is a counterspell, Yogg casts a random spell again (Proc Counterspell), Twisting Nether (Finally clears board, two scientists pull a counterspell and Effigy), random spell again (Proc Counterspell). Now Yogg might just BM the opponent/make me lose by casting more spells but what I listed before is just what is needed. Next play is Eater of Secrets>Archmage Antonidas>Sorcerer's Apprentice>Sorcerer's Apprentice>Echo of Medivh(5 mana left)>Sorcerer's Apprentice>Sorcerer's Apprentice>Echo of Medivh(0 mana left)>Sorcerer's Apprentice>Shoot dem Free Fireballs to the enemy's face.

What do you think of this?