Please find a decent but ultimately not strong enough Mecha'thun OTK deck.
The ultimate win condition of this deck is to play N'Zoth, the Corruptor and then Bogbeam an Explosive Sheep in order to start a Deathrattle sequence: The sequence does 13 Damage, taking out Mecha'thun in the process.
Why Explosive Sheep and Fatespinner are the best deathrattles to use:
When viewing this deck it is logical to question why these deathrattles in particular. The answer is plainly to avoid a Sylvanas Windrunner counter-play.
This combination, if Bogbeam is on an Explosive Sheep, does 2, 2, 3 then 3 damage to all minions on board. When a Sylvanas Windrunner is active on board, the sequence of deathrattles prevents Sylvanas Windrunner from stealing Mecha'thun halfway through the concurrent explosions. I believe it is therefore the only safe combination of deathrattles to use in this kind of deck.
So what of the other minions and spells:
The deck has as much efficient Ramp as possible in order to keep up with the quickest tempo decks. Hopefully the four dragons are enough to warrant keeping Jungle Giants, Breath of Dreams in the mulligan, especially with Doomsayer to ensure early control.
The deck has flexible removal spells, Wrath can be used to draw, can be used with a Fatespinner to clear, and can also play the part of Bogbeam if N'Zoth, the Corruptor costs 0 on the last turn. Ultimate Infestation [/card]should be changed for Nourish if you're playing against a lot of Fatigue Rogues and [card]Branching Paths is used for flexibility, enabling for wins against some aggro some of the time.
A note on Foe Reaper 4000: It saves quite a few games; especially with Zilliax, acting as a full heal.
So yeah, I hope you enjoy. I'll add general strategy to the guide if required. Let me know what you think.
All Good Things,
Took away the dragon package and Ultimate Infestation. The deck is stronger now as Doomsayer, Branching Paths and Nourish are all flexible enough options to be useful against most classes and archetypes.
I particularly found that I was losing against Demon Hunter and Fatigue Rogue. Demon Hunter is controllable now with the extra armor-gain capabilities, and Mill-Rogue can be handled by using Nourish for Mana instead of draw.
A last note: Tunnel Blaster has been added for situations where Moonfire has to be used before the last turn. It is a small risk as Devolve affects can add extra deathrattles to your board at the end, but it is a nuisance-enough card to warrant the addition.
Please keep in mind that all Deathrattles in the combo do not have to be played if they cost 0: They can be kept to be played in the last turn all in one.
Re-inserted a dragon package with Ysera and Primordial Drakes. Ysera in my opinion is still on of the strongest neutral Legendaries allowing strategies to stall, clear or control the board. Primordial Drake is important as it has Taunt and combined with Explosive Sheep can just enough clearing power. Took away Fandral an most Choose One cards are they struggle with consistency.
* Take note, against a Weapon-based Meta I would change Ysera for a Gluttonous Ooze.