Path Of The Molten Core

Forged by the flames of fury, the followers of the Path of the Molten Core channel an inner wrath so great, that it manifests in the form of flames to consume their foes on their quest to be satiated. 

Magma Rage

Starting at 3rd level, when you enter a rage, you become fueled by the power of molten lava. While raging, your attacks deal additional fire damage equal to your proficiency bonus. Additionally, when you take damage from an attack, you can use your reaction to deal fire damage equal to half your barbarian level to the attacker. While you are raging, if the target has resistance to fire damage, you ignore that resistance. 

Volcanic Aura

Beginning at 6th level, you radiate intense heat and smoke. When raging, at the beginning of your turn, each creature within 5 feet of you must succeed on a Constitution saving throw, taking 1d6 fire damage on a failure. The DC for this saving throw is equal to 8 + your Constitution modifier + your proficiency bonus. You are also immune to fire damage while raging. In addition, while raging, any fire damage you would deal ignores immunity to fire. All fire damage dealt this way is halved if the target would normally be immune to fire. 

At higher levels. The damage taken on a failure increases to 2d6 at 12th level, and 3d6 at 18th level.

Molten Weapon

At 10th level, you can infuse your weapon with molten lava as a bonus action. On your next attack, your weapon deals an additional 2d6 fire damage, and the target must make a Dexterity saving throw (DC = 8 + your proficiency bonus + your Strength or Dexterity modifier) or be set on fire, taking an additional 1d6 fire damage at the start of each of its turns until it uses an action to put out the flames.

Once you use this feature, you must complete a short or long rest before using it again.

Volcanic Fury

At 14th level, when you score a critical hit while raging, you can choose to unleash a volcanic eruption of power. All enemies within 30 feet of you must make a Dexterity saving throw (DC = 8 + your proficiency bonus + your Constitution modifier), taking 4d6 fire damage on a failure and half damage on a success. Additionally, any flammable objects in the area ignite and burn for 1 minute. Once you use this feature, you must complete a long rest before using it again.