A few tricks to this one..

First of all DONT knock his life total down below 142 until right at the end of the game.

If you do he'll play molten giants for 10 or less and flood the board and you dont want that till he's one turn from dieing.

The stategy here is to embiggen and play your untargetable minions that he cant copy with his hero power.

When you do play GORU he'll copy that one exclusively even over his 8/8's which are better. His copies though wont have taunt and wont be buffed by your embiggen's.

You just need to build a big board.. kill his minions till you can double savage roar him (which wont kill him in one turn but you'll do him in next turn). Vargoth will help you buff your guys a LOT so have him in play when you use blessing of the ancients, power of the wild, gift of the wild.

I included one witch's cauldron so you might be able to pull a bloodlust, windfury , hex to make the end turns easier.