Hearthpwn

For the most part we use a draw heavy deck and wait till we get Hemet, Jungle Hunter to blow up are deck.

For this deck we have more than one way for use to trigger Mecha'thun. 

For the first combo we need 1x Innervate, 1xNaturalize, and Mecha'thun.  once u have these cards in your hand you can then blow up your deck with Hemet, Jungle Hunter and dump your hand. The order would be Mecha'thun then innervate then naturalize Mecha'thun. For this combo, Galvanizer Can be used Instead of Innervate. 

For the Second combo we need Flobbidinous Floop , 1xStarfall,  and Mecha'thun. To pull off this combo you can Hemet, Jungle Hunter any time since all of these cards are above 4 mana (Hemet, Jungle Hunter destroys anything 3 mana and below). After we Hemet, Jungle Hunterwe can dump are hand but we have to make sure that the last minion played is  Mecha'thun so that  Flobbidinous Floop will copy the card. so the last 2 cards in your hand will be Flobbidinous Floop and Starfall. with that you can just play Flobbidinous Floop  and  Starfall it. 

So other than getting killed by aggro, another counter may be just Counterspell. they wait till we kill are deck when we got the 3 cards in hand they can just Counterspell and lose are Innervate. another one might be Spellbender since we do target Mecha'thun or Flobbidinous Floop to win the game. only way I can think of getting through them is to keep an additional Innervate and Naturalize in hand when playing against mage.