Mulligan for mana tide totem.
On 3 mana cast one of the 0 cost spells given to you to destroy his 2 dudes and play Mana tide
He will either have a removal and waste it on the mana tide, or he will not have removal in which case you're winning anyway.
For the rest of the game just play smart. His only 'very' good board clear against this is defile, but that won't save him from questing adventurer and Frostowolf.
Possible additions: sea giant? I didnt use it so you probably dont need it/it might not be good
Play smart: On 8 mana he will have enough mana to cast his big board clear.