Your character has been possessed by a malevolent spirit called a Wendigo, likely due to eating human or demi-human flesh. You can attempt to harness this spirits abilities, but at great cost.

Your character will take on a guant, almost emancipated look, with an ashy, greyish skin tone, and sunken features. They feel perpetually hungry and never seem to be 'full'.

You gain Darkvision 60'

Choose two cantrips from the Warlock spell list. You can cast them at will.

In addition, choose one 1st level spell from the Warlock spell list. You learn that spell and can cast it at its lowest level. Once you cast it, you must finish a long rest before you can cast it again using this feat. (DC 10)

Charisma is your spellcasting ability for these spells.

Mimicry. Your character can mimic animal sounds and humanoid voices. You have advantage to deception checks that involve mimicry, and a creature that hears the sounds can tell they are imitations with a successful DC 18 Wisdom (Insight) check.

Ambusher. By activating this ability, your character has advantage on attacks against targets who are unaware of its presence for the remainder of that combat. (DC 14) (DC increases by +2 per use until you have had a long rest)

Hunter. By activating this ability, your character has advantage on Dexterity (Stealth), Wisdom (Survival) and Wisdom (Perception) checks for the next hour. (DC 14)  (DC increases by +2 per use until you have had a long rest)

At Higher Levels. When your character reaches 5th level, you can maintain this ability on the spell for up to 8 hours (DC 17). When your character reaches 9th level, , you can maintain this ability for up to 24 hours (DC 19). 

Expending all of any of the following categories result in the Wendigo attempting to posses the host (DC20): Spell slots, Ki points, Rages, Grit points or Superiority dice.

Using any of the features with a listed DC allows the Wendigo to attempt to possess the host. The character must succeed on a Wisdom saving throw at the specified level or be possessed by the wendigo;  the target is incapacitated and loses control of its body. The wendigo now controls the body but doesn't deprive the target of awareness. The characters transforms into a Elder Wendigo (CR15). It will remain in this form for 24 hours or until reduced to 0 hit points, at which point your character will revert to their normal form, unconcious with 1 hp, and 5 levels of exhaustion. During this time it will feed on any living thing in the area, with a preferance for human and demi-human flesh. If possible it will hunt those closest to your character. Upon returning to normal, all bonuses and penalties from this feat are inert for the next 24 hours. 

A Greater Restoration spell will temporarily banish the Wendigo, as if it had 0 hit points. A lesser restoration spell with allow the host to make a WIS save (DC 20) to banish the Wendigo, as if it had 0 hit points.