Fireshaper is always the highest priority treasure, Wither the Weak is significantly less consistent and will almost never give you the gas you need. When you really pop off is if you can get either Khadgar’s Orb or Ooops, All Spells! The latter being more consistent as you can thin your deck. If you get Ooops, All Spells!, try to choose minion treasures over more expensive spells. The only spell treasures you want are Bag of Coins and Mindpocalypse.