The OTK combo:
Having used Anka, the Buried prior to the combo turn, Mecha'thun will be a 1 mana 1/1, which enables the combo: Firstly play a Wild Pyromancer and Myra's Unstable Element to empty the deck and damage the Pyromancer for 1 health. Then play the cheap Mecha'thun and finish the combo off by playing Secret Passage. When the Secret Passage is played, the remaining cards in your hand will go into "the passage" and will therefore neither be in your hand nor your deck. And having played Myra's Unstable Element, your deck will be empty, which enables the Mecha'thun Deathrattle when the Wild Pyromancer kills it. The only bottleneck of the deck, is the requirement of having no minions on the board with more than 2 health (the Pyromancer can deal with maximum 2 health).
The main focus of the deck is trying to OTK your opponent using the mighty Mecha'thun. To draw into the combo, the deck features a battlecry/combo package with the main focus of drawing through your deck using Field Contact. To do this efficiently the Efficient Octobots can be triggered using tools like Backstab and Brainfreeze (both of which are also great against aggro match-ups). Furthermore, Lorekeeper Polkelt and Tealon Fordring both contribute to more consistent draws. For extra versatility Scabbs Cutterbutter is also included in the list. Lastly cards like Armor Vendor and Cloak of Shadows will help you survive until the combo is ready.