Firefist Phoenix 

Fire of fury

Once per long rest you enter a state where you can add the damage you have taken to your HP to your attacks as magical fire damage. For example if you have 34 maximum hitpoints but you currently only have 14, you can add 20 damage.

Every turn in this state you take 1d4 times the number of turns you have bean in the state and an extra d4 for each attack taken in the state.

The state ends if you are restored to full HP or are not attacked for two turns or if you go unconscious or if you end it with an action.

Everburn

At 6th level when you go below 0HP and you are in the Burning Rage state you do not go unconscious but remain fully active and gain immunity to fire damage including your own . However gain immunity to fire damage including your own but you still must roll death saving throws. If you end your Burning rage you immediately go unconscious if you still have zero health.

Phoenix

When burning rage is activated the character also gains a pair of flaming bird wings with a flying speed of 60ft.

One with the flames

You can Burn without needing to wait for a long rest if you are in daylight.