Path of the Demon

Any Barbarian feeds some dark part of themselves when they rage, losing themselves to primal impulses just enough to draw strength from them. But sometimes the source of these instincts is more malevolent. Whether as the result of a tainted bloodline, unfortunate side effect of fiendish possession, or simply achieved by crossing the line from fearsome into monstrous, some souls are imbued with demonic essence. Many try to fight this affliction, some cannot and simply must live with the damage it inflicts on their bodies. But those that embrace this forbidden power, that learn to let it feed on their rage, gain unholy strength and fury. They grow into a being of pure power and cruelty, that just wants to watch the world burn. 

Demonic Rage

3rd-level Path of the Demon feature

When you enter your rage, your demonic abilities manifest. When you enter your rage you can decide to enter a demonic rage instead. While in demonic rage you gain all the benefits of a normal rage as well as the following:

• Your size category becomes large, given it wasn't large already, and your appearance grows more demonic.
• You gain a natural weapon of your choice, be it claws, fangs, horns, hooves, or similar. This weapon has a reach of 5ft. and deals bludgeoning, piercing, or slashing damage (your choice), and it uses strength for attack and damage rolls. This natural weapon also counts as magical for the purpose of overcoming immunities and resistances. 
• Once per turn when you when you attack with a natural weapon granted by this feature as part of your attack action, you can make one additional attack as a bonus action. 
• Whenever you damage a creature with a melee weapon attack using strength, you regain a number of hit points equal to your rage damage bonus.

Whenever your demonic rage ends you take damage equal to your barbarian level+ twice the number of rounds you spent in your demonic rage. This damage is unavoidable and cannot be prevented in any way. All restrictions and limitations of rage still apply to demonic rage. Any ability that enhances rage also benefits you when in demonic rage.

Abyssal Fortitude

6th level Path of the Demon Feature

You become closer to Demons. While in demonic rage you gain immunity to poison damage and the poisoned condition, as well as resistance to cold, fire, and lightning. 

Unleash the Beast

10th-level Path of the Demon feature

 You can now momentarily tap into the endless rage of the Abyss, at the risk of losing your mind. Once per long rest you can enter your Demonic Rage without expending a use of rage. 

When you enter your demonic rage this way your mind is consumed by bloodlust and you can only move and make melee attacks on your turn. If you end your turn without attacking a creature, you immediately move your full speed towards the nearest creature (if necessary) and make one attack with your natural weapon against them. If you don't hit the creature, or are incapable of attacking anyone, your demonic rage immediately ends. 

Demonic Ascendance

14th-level Path of the Demon feature

 You've fully accepted the demonic essence into yourself. You gain the following benefits:

• Your physical appearance permanently changes to take on more demonic aspects, although not enough to rouse outward suspicion in most.
• Your creature type changes to Demon (Fiend) if it wasn't that already. Spells that affect fiends of a certain CR do not affect you.
• You gain the benefits of your Abyssal Fortitude feature even when not raging.
• You no longer take damage when your Demonic Rage ends.
• While in your Demonic Rage you gain a flying speed of 30 feet, as spectral demonic wings sprout from your back.