Path of Ancient Madness

There are powers that exist throughout the multiverse that are all but unknowable to the mortals that inhabit the material plane. When faced with these existences firsthand, most creatures lose their grip on reality or simply die on the spot. A barbarian that walks the Path of Ancient Madness is the exception to the rule, having stood strong in the face of a world-shattering truth. No one can escape from such an experience truly unchanged, however. The rage of a Barbarian of Ancient Madness comes from that latent seed of eldritch power lying within them after an encounter with the inconceivable. When they rage, the twist the world around them to match the echoes of the aberrant that echo in their head. 

Shifting Visage

When you adopt this path at 3rd level, your facial features become soft and easily reshaped as you slowly fall under the influence of eldritch powers. You gain advantage on Charisma (Deception) checks made to pretend to be someone you aren't. Additionally, you can use your action to remold your features, changing your appearance and gaining the benefits of the Disguise Self spell. The Intelligence (Investigation) check DC is equal to 8 + your proficiency bonus + your Constitution modifier. 

Maddening Fury

At 3rd level, your rage becomes a conduit for the horrors you've witnessed. While you're raging, you may subject a creature to horrific visions of the beyond whenever you hit it with a melee weapon attack. The target must succeed on an Intelligence saving throw (DC 8 + your proficiency bonus + your Constitution modifier) or be frightened by you for one minute as it has glimpses of existences beyond its understanding. On the end of each of the affected creature's turns, it may repeat the saving throw, ending the effect on itself on a successful save. 

You may use this feature a number of times equal to your proficiency bonus. Uses are only expended if the creature fails the saving throw. You regain all expended uses when you finish a long rest. 

Aberrant Will

Beginning at 6th level, your experience with aberrant powers has hardened your mind against mental attacks. If you would make an Intelligence, Wisdom, or Charisma saving throw, you may use your reaction to gain advantage on that saving throw. 

You may use this feature a number of times equal to your proficiency bonus. You regain all expended uses whenever you finish a long rest. 

Intensified Visions

At 10th level, the visions you inflict during your rage grow more intense. Creatures that fail the saving throw against your Maddening Fury feature are stunned until start of your next turn. They still suffer the frightened condition as normal. 

Insanity Manifest

At 14th level, your rage begins reflecting the true terrors of its eldritch source. When you enter your rage, you may choose to create a 15 foot radius sphere centered on yourself that lasts until you exit your rage. The sphere moves with you, and ground within it is difficult terrain for creatures hostile to you as it transforms into a roiling mass of grasping tentacles and gaping maws. Your melee weapon attacks do an additional 2d6 psychic damage while the sphere persists. Additionally, whenever an enemy creature ends its turn in the sphere, it must succeed on a Dexterity saving throw (DC = 8 + your proficiency bonus + your Constitution modifier) or be pulled  up to 15 feet towards you, stopping once it is within 5 feet of you or if it would enter a space occupied by another creature.

 You may use this ability once, after which you must finish a long rest before you can use it again.