I was thinking that fire needs a bit more permanents.
Firewall___4
Firewall gains one charge every three creatures/permanents destroyed in a turn. With one charge, firewall boosts all fire creature attack stats by one.
Let's say you kill five creatures with rain of fire, and destroy one permanent with deflagration.
You would get two charges, and you have three phoenixes. They would have 7/1 stats, and with firewall, you get 9/1, 9/1, 9/1 in total.
This could be used with Earthquake, Ash Eater spamming, and maybe Fire Spirits really well.
Maybe if upgraded, it does the same thing but gains a charge every two cards destroyed.