Path of the Chaotic Flame

Taking this path requires a Tiefling to spend a lot of time using their rage to ignite a spectral flame deep within them, allowing this flame to grow overtime, and eventually allowing them to let this flame absorb them, causing their rage to get stronger and to burn hotter. 

Fiery Rage

Starting at 3rd level, while raging,  you also gain the following benefits:

• Your Rage Damage deals Fire damage instead of your weapon's damage. Your Rage Damage increases to 1d4. It increases to 1d6 at 9th level, and 1d8 at 16th level. On a critical hit, all the weapon damage is Fire damage. 
• You shed bright light in a 20 foot radius, and dim light for an additional 20 feet.
• When a creature within 5 feet of you deals damage to you, they take Fire damage equal to your Rage Damage.

Radiating Chaos

Starting at 6th level, a fiery and chaos inducing aura surrounds you while you rage. While you Rage, every creature of your choice within 20 feet of you are affected by the following things: 

• When any creature enters the aura for the first time on their turn, or if they start their turn in the aura, they take your Rage damage in Fire damage.
• At the beginning of your turn, every creature(including you) must make a Wisdom save (DC = 8 + Constitution modifier). On a failed save, they must use their reaction to make a melee attack against the closest creature in their range.
• You have the effects of the Dragon's Breath spell, using Fire damage.

Endless Burn

Starting at 10th level, when you Rage, you gain the following benefits: 

• Any Fire damage you deal is normally effective against creatures who resist it and is only resisted by creatures normally immune.
• You gain full immunity to Fire damage.
• You gain resistance to Poison damage, and have advantage against being poisoned.
• Any diseases afflicting you are cured, and you are immune to diseases.

Berserk

Starting at 14th level, you gain the ability to go full berserk when you rage. When you Rage, you can choose to instead go Berserk. You can also change from normal Rage to Berserk as a bonus action. If you do this, you gain the following benefits and drawbacks: 

Benefits: 

• You gain the basic features of Rage. Other than the new effects, it acts exactly like Rage.
• All friendly creatures in your Radiating Chaos aura get advantage on Melee attacks. 
• You get advantage on Melee attacks. 
• All your Melee attacks deal all Fire damage, and can't be resisted or nullified.
• You gain resistance to all damage.
• You can make 1 extra Melee attack as a Bonus Action on each of your turns.
• The DC for Radiating Chaos aura becomes 8 + proficiency bonus + Constitution modifier
• You deal double Rage damage. (Only triple on Crit, not quad)

Drawbacks: 

• You gain 1 level of exhaustion when you leave Rage.
• Any non friendly creature in your Radiating Chaos aura instantly starts targeting you with their attacks.
• All creatures in your Radiating Chaos aura have advantage on attack rolls against you.
• You take 1d8 psychic damage at the beginning of each of your turns.

You can choose to end your Berserk without ending your Rage as a bonus action on your turn.