How about taking out the 5 fire spirits and throwing in 5 lava golems?
P.S. If you change the mark to earth, will it not be a mono-deck?
It would still be mono-fire.
5 fire golems would work better, but if you only had a mark to feed their growth, you might not be able to grow all of them every turn, leaving them at low health, which was one of the weaknesses of this deck.