Path of Blood-Fury

The touch of a fiend corrupts the material plane, corroding morals and burning away the mental resiliences of its victims. Those who walk the Path of the Abyss are those of which fiends have permeated into their very souls, tying them to the infernal planes through flesh and mind. Their rage is fueled with fiendish energy, tying its creator with various types of fiends.

Consider how your barbarian found themselves connected to the abyssal plane. The Abyssal Origin table offers some examples.

d4Abyssal Origin
1You were born with a fiendish connection, a connection much stronger than with other tieflings or fiend-touched creatures.
2You share your body with a lingering fiendish spirit, which manifests through your rage.
3You have consumed nutrients from the infernal planes, permanently altering your physiology.
4You were sacrificed, willingly or unwillingly, to summon a fiend into the material plane. Somehow you survived, connecting you to the fiend that still roams this plane.

Abyssal Mark

Upon taking this path at 3rd level, you awaken your connection to the pits of hell upon entering a rage. Until your rage ends, you can speak Infernal and gain one of the following benefits. If this benefit provides you a natural weapon, you are proficient in it and you add your Strength modifier to the attack and damage rolls when you attack with it. If one of these benefits require a saving throw, the DC equals 8 + your proficiency bonus + your Constitution modifier.

Each time you gain a level in this class, you can choose to change the benefit you have from this feature for another benefit provided

Claimed Body

Also at 3rd level, you can’t be possessed while raging, and can spend your reaction to enter a rage when a creature would attempt to possess your body.

Reap the Wrongdoers

At 6th level, you can devour part of a creature's soul to invigorate yourself. When you reduce a creature to 0 hit points, you gain an amount of temporary hit points equal to 1d12 + half your level in this class. You can also use this feature as a reaction when a creature within 30 feet of you would be brought to 0 hit points, but doing so grants you half as much temporary hit points.

Additionally, if you are smaller than Large, you and anything you are wearing become Large when you enter a rage. If you lack the room to become Large, your size doesn't change.

Corrupt the Damned

At 10th level, you can bend your foes spirits so that they serve your purposes for a short time. Upon hitting a creature, choose another you can see within 30 feet of you. Until the end of your next turn, the creature you hit has advantage on attack rolls against your target, is hostile to them, and has disadvantage on attack rolls against any other creatures.

You can use this feature once per rage.

Aspect of Sin

At 14th level, you can additionally manifest one of the following trait while raging.

Each time you gain a level in this class, you can choose to change the benefit you have from this feature for another.