Hard mulligan for Embiggen and restart if you don't have it by turn 1, otherwise the 3 mana minions will be destroyed, and you don't really want that. Also restart if you don't have Mossy Horror by turn 7. Otherwise, go to town on him. I managed to win on my first try after maybe a dozen restarts, in part because I was lucky enough to have Mossy Horror in time to clear the trapped souls.