phanTasm's (Secret?) Mecha'thun Hunter Theorycraft Deck

Subject 9: Subject 9 is generally a good Mulligan card, as it draws a lot of cards from your deck and those said cards can help you stall and protect yourself until you can pull off your combo. It also has synergy with Gadgetzan Auctioneer.

Gadgetzan Auctioneer: Gadgetzan Auctioneer is also quite a good Mulligan card, as it is the main source of card draw in your deck, and a chain of draws over a few turns can easily be started once you have the right cards.

Master's Call: Master's Call allows you to draw important key minions in your deck to deal with certain threats and made certain decisions, and that is quite necessary for this deck to work.

Animal Companion: Animal Companion is one of the few early game card in this deck, and can provide decent coverage and stalling for your other cards.

Subject 9: See General.

Explosive Trap: Explosive Trap is also quite a good Mulligan card, as it can protect against those low HP aggro threats, and is particularly strong against Zoolock.

Master's Call: See General.

Zilliax: Zilliax is the only card in the deck that can both heal and damage enemies, and is also the only Taunt minion in the deck. If you magnetise this card with the Mechanical Dragon, you can gain up to 10HP and have a real powerhouse on the board, which is good against those small minions that aggro decks use.