Path of the Pyroclast

As a Barbarian of the Path of the Pyroclast, you gain access to lots of fiery abilities both in and out of your rage, foremost among them are your shifting states. these states each have a specific ability and can be shifted between when certain circumstances are met. these are the core of your abilities, though outside of rage you still embody the heat of the burning mountains. those who follow this path are versatile and change in the blink of an eye, going from an immovable mountain to a flying tsunami of flames in an instant.

Volcanic Rage

Starting when you choose this path at 3rd level, you gain resistance to fire damage and access to the following states, additionally, when you rage you may choose to go into Dormant state.

Dormant. Immediately when entering Dormant state you gain twice your level in temporary hit points. while in Dormant state you no longer have advantage on Strength checks but gain advantage on all saving throws. when you run out of temporary hit points while in Dormant state you erupt, dealing fire damage equal to double your level to all creatures within 10 ft. of you. when this happens you can choose to take fire damage equal to your level or end your rage (damage taken this way cannot be reduced in any way). if you take the damage you enter Active state.

Active. Every time you hit with an attack, you deal an additional 1d6 (becomes 2d6 10th level) fire damage to the target, you gain temporary hit points equal to half the fire damage dealt. additionally whenever you kill a creature or land a critical hit you may choose to erupt, when you erupt, all creatures within 15 ft. of you take twice your level in fire damage and you take half that much fire damage, when you erupt you enter Erupting state. (damage taken this way cannot be reduced in any way)

Erupting. You lose all resistances while in Erupting state and gain immunity to fire damage. whenever you deal damage to a creature while erupting you may choose to deal additional fire damage equal to double your level to the target and half that to all creatures within 5 ft. of the target. 

Molten Soul

Beginning at 6th level, you embody the heat of the burning mountains, you gain resistance to cold damage, and are immune to cold effects like frostbite. all creatures within 5ft. of you gain access to these features, but lose it as soon as they leave your range (increases to 10 ft. at 10th level). Additionally you can conjure flames from your skin that light flammable objects that arent being worn or carried.

Scalding Pressure

Beginning at 10th level, as a reaction to being hit before you know the damage you may choose to ignore any resistances you have to that damage type to deal half that much damage back as fire damage. 

Additionally, all fire damage you deal ignores resistance but does not affect immunity.

Tectonic Rage

Starting at 14th level, your states gain additional abilities.

Dormant. When you are hit with a critical hit, reduce the damage you take by half (stacks with resistances) additionally, whenever you kill a creature gain temporary hit points equal to its CR (minimum 1)

Active. When you are hit with a critical hit you may reduce the damage by your level to enter Dormant state, or increase it by your level to Erupt, and enter Erupting state.

Erupting. All enemies within 5 ft. of you becomes vulnerable to fire damage, if they were immune to fire damage they instead become resistant. if you would be reduced to 0 hit points while in Erupting state you may instead be reduced to 1 and enter Dormant state, if you do this you gain 1 level of exhaustion.