I recommend keeping the convert to spell in your deck if you have it because you fight fire school Bosses many times.
If you have Sun Bird as your best spell use/buy treasure cards from the bazaar because the bosses are very difficult and you can't kill them with only sun bird.
If you have any training points go Krok and train balance spells (for lvls 25+)
School Advice, Lvls 20+
spell in your deck if you have it because you fight fire school Bosses many times.