This deck wins by removing all the enemy threats and milling through his deck. Giant fin has a 50 card deck but draw 3 cards a turn. meaning you need to survive about 16 turns.
Mull for your early game cards and tap into removal. Play taunts when he has a weak board to save removal for when hes loaded up. you can be somewhat patient. Be mindful of warleader & coldlight seer (the +2 health guy) coming out next turn if your leaving guys alive. but the Ai isnt very smart about when to play these so its not that bad. later play Doomsayer after youve cleared the board to skip his next turn. Save dark bomb for important spot removal like warleader. Tide caller and Oldmurk eye can even win the game early on but also trade well and combo with shadowflame*.
If you dont have all the cards to make this version you can substitute a few things and still have a chance.
With a little luck im sure youll beat him in a couple tries. Goodluck