Mulligans
General Mulligans
Clears, Hemet, and combo breakers
Aggro Mulligans
Little guys, clears, and draw
Control Mulligans
The combo and hope your opponent can't clear a turn 10 Mecha'Thun. If you think they would be able to without polymorphing or silencing it then maneuver so you have no cards in hand or deck so Mecha'Thun can be cleared like that. Also Howlfiend-Treachery-Defile to destroy their ability to polymorph or silence your Mecha'ThunUse Hemet to thin your deck down to just Mecha’Thun and Cataclysm, then play Mecha’Thun and then Cataclysm. Use boardclears and stuff to try to get your opponent to concede on the side.