Path of the Roaring Flame

This subclass will allow your barbarian to light themselves on fire, doing fire damage with attacks and even being able to breathe fire.

Ignite

When taking this subclass at 3rd level when you enter a rage you can use your action to Ignite yourself. Once activated all creatures within 5ft of you take damage equal to your half of your barbarian level (rounded down). Once you attack someone on your turn, that target takes  1d8 fire damage. This damage increases to 2d8 upon reaching level 10 and finally 3d8 at 14th level. Exiting an Ignited rage gives you 1 level of exhaustion, as your body recovers from overheating.

Feel the Burn

Reaching 6th level you become more used to the affects of your Ignition. while Ignite is active you have resistance to fire damage.

Fan the Flames

Upon reaching 10th level Your Ignition sparks fear into your foes. When activating Ignite all enemies that can see you must make a wisdom saving throw of 8+proficiency+constitution mod, or be frightened by you for 1 hour. The target can make another check on each of it's subsequent turns. If the target makes the save they cannot be frightened by you again for 24 hours.

Immolation

Once reaching 10th level when you reduce a hostile creature to zero hitpoints while in an ignited rage, you burst fire in a 10ft area around you, dealing fire damage equal to your barbarian level to all hostile foes in the burst, if you are not ignited when you knock the creature to zero hitpoints you automatically ignite and burst as normal. You may choose to ignore the automatic Ignite but by doing so you do not activate Immolation.

Roar

Upon reaching 14th level you gain the ability to breathe fire at your enemies. Using your bonus action you exhale a ten foot cone of fire out in front of you. The target or targets trapped in the cone must make a dexterity saving throw of 8+proficiency+constitution mod. Or they take 6d6+half your barbarian level rounded down, fire damage and half damage if they save. Roar can only be used a number of times per day equal to your constitution modifier (minimum of 1) per long rest.