Path of the Abyss

 Some barbarians draw their fury from primal spirits or ancient traditions. Others have gazed into the infinite darkness of the Abyss and emerged forever changed. Whether marked by a demonic curse, infused with abyssal essence, or born of an unholy bloodline, these warriors surrender themselves to a rage that twists flesh and soul alike. As their fury grows, so too does the Abyss's hold upon them, until they become living echoes of its boundless chaos.

Level 3: Abyssal Rage

 3rd-level Path of the Abyss feature

 When your Rage consumes you, the corrupting power of the Abyss manifests through your body, warping your flesh into a weapon of relentless destruction. You gain the following benefits:

 Evil Claws. You can transform your arms and hands into monstrous, abyssal appendages at will (no action required), or return them to their normal appearance. While transformed, you can roll 2d6 in place of the normal damage of your Unarmed Strike. In addition, whenever you deal damage with your Unarmed Strike, it can deal your choice of Force damage or its normal damage type.

 Demonic Rush. When you activate your Rage and as a Bonus Action while your Rage is active, you can make an Unarmed Strike.

 Eyes of the Abyss. While your Rage is active, you have Darkvision with a range of 60 feet. If you already have Darkvision, its range increases by 60 feet while your Rage is active.

Level 3: Abyssal Tongue

 3rd-level Path of the Abyss feature

 The whispers of the Abyss become your own.

 You can speak, read, and write Abyssal. Additionally, you can communicate telepathically with any creature within 60 feet of you that understands Abyssal.

Level 6: Entropic Rupture

 6th-level Path of the Abyss feature

 Your fury tears at the fabric of reality itself, allowing the raw entropy of the Abyss to erupt from beneath your feet and consume everything nearby.

 As an Action while your Rage is active, you can strike the ground with supernatural might and tear open a rift into the Abyss, unleashing a burst of entropic energy around you. Each creature in a 10-foot emanation originating from you must make a Dexterity saving throw (DC = 8 + your proficiency bonus + your Strength modifier). On a failed save, a creature takes Force damage and is pushed 10 feet away from you. On a successful save, a creature takes half as much damage only. To determine the Force damage, roll a number of d6s equal to twice your Rage Damage bonus, and add them together.
 You can use this feature a number of times equal to your Strength modifier (minimum of once). You regain one expended use when you finish a Short Rest, and all expended uses when you finish a Long Rest.

Level 10: Demonic Resilience

 10th-level Path of the Abyss feature

 The corruption within your body deepens, hardening your flesh against mortal harm until it resembles that of the fiends from which your power was born.

 You have Resistance to Cold, Fire, and Lightning damage while your Rage is active. In addition, you have immunity to Poison damage and to the Poisoned Condition while your Rage is active. If you're Poisoned when you enter your Rage, the condition ends on you.

Level 14: Abyssal Suffusion

 14th-level Path of the Abyss feature

 The Abyss no longer merely fuels your Rage—it has become an inseparable part of your being. Its corrupting essence courses through every fiber of your body, granting you the terrifying resilience and destructive might of a true demon. You gain the following benefits:

 Claws of Oblivion. While transformed by your Evil Claws feature, you can roll 3d6 for the damage of your Unarmed Strike, instead of 2d6.

 Entropic Disaster. You add your Strength modifier to the damage dealt by your Entropic Rupture feature. In addition, its area becomes a 15-foot emanation, and creatures are pushed 15 feet away from you on a failed save.

 Magic Resistance. You have Advantage on saving throws against spells and other magical effects while your Rage is Active. If you're under the influence of any spell or magical effect when you enter your Rage, you can immediately repeat the saving throw against that effect to end it on yourself.