Hearthpwn

What is the combo here?

It looks like Celestial Alignment to make Mecha-Thun cost 1, next turn Twig and Sapience, then burn whole deck with overflows and malygos.

Play floop and first seeds for mana if you run low 

Play illusionist(survive fatigue just in case) mechathun and second seeds as last cards, mechathun deathrattle triggers while all the minions are dead for the OTK

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This list is no good IMO. I would run something with Anacondra instead for reliability (never run out of mana, etc etc.) 

You could probably stick the mechathun kit into a jambre-inspired anacondra druid as a second win condition, the mecha-thun kit only *requires* 2 cards (mechathun and seeds obviously) but would be better with maybe 5 so you can get floops and a second copy of poison seeds just in case any issue with mana somehow(?) shows up

Wish I could craft this deck, it'd be pretty weak in wild probably but definitely fun