I couldn't finish 'em. Looks like this's gonna get complicated.
Firemane itself will only ever cast Fire. However, at 80%, 60%, and 40% HP, the bonfire in the center of the room will roar to life and the torches lining the outside will start spawning Damantus and Noxius wisps. Each torch will spawn four Damantus and one Noxius, which will slowly start moving towards the bonfire one at a time. Should they reach the bonfire, they will explode using Scorched Earth, dealing damage to the entire party. The Damantus explosions are fairly weak, but the Noxius deal considerable damage.
Only one torch will activate at 80%, then two at 60% and finally all three at 40%. It is recommended to for the party to at least kill the Noxius wisps - while the Damantus explosions can be fairly easy to handle, the Noxius can overwhelm the healer, especially in later stages where there will be several explosions in quick succession.
Upon Firemane's defeat, the bonfire will erupt into an Aetherial Flow, allowing the party to teleport deeper into the dungeon.