Aleth, Unchained

Legendary Resistance (3/Day). If the wendigo fails a saving throw, it can choose to succeed instead.

War-torn Resilience. Aleth takes 1 damage, regardless of attack roll, for any attack made with a non-magical weapon. Magical spells deal full damage, and weapons made of Adamantium deal double damage.

Powerful Build. Aleth counts as one size larger when determining her carrying capacity and the weight she can push, drag, or lift. 

Soul Magic. Aleth does not use material components for her spells. Instead, she takes 2d12 + (5 times the level of the spell) damage. This damage cannot be reduced in any way.

Essence Theft. Aleth can consume a dead enemy to gain temporary hitpoints equal to 2d8 + (2 times their Player Level or CR). 

Magic Weapons. Aleth's attacks are magical. Additionally, her magical chain gauntlets count as both Martial weapons, and as her Pact of the Blade weapon for the purposes of Invocations. The properties of the chains themselves are Heavy and Reach.

Multiattack. Aleth makes three attacks: one with her bite and two with her claws.

Bite. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage.

Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Chain Grapple. Melee Weapon Attack: +14, reach 20 ft., one target. On a hit, the target must make a strength save, DC 19. On a failed save, Aleth can choose to follow up with a claw attack that hits with advantage. If the target is of size Huge or larger, she is pulled to the target's location. If the target is of size Large or smaller, they are pulled to her location. If she does not choose to follow up, the target is instead grappled at range.

Swallow. Aleth makes one bite attack against a Medium or smaller creature she is grappling. If the attack hits, the target takes the bite's damage, then must make either a Strength or Dexterity save, DC 19. On a fail, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, and it has total cover against attacks and other effects outside the wendigo.

If Aleth takes 30 damage or more on a single turn from a creature inside her, she must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of her. If Aleth dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

For multiple creatures, Aleth must make an Athletics check, DC 20, or suffer disadvantage on Dexterity Rolls.

Change Shape. The wendigo magically polymorphs into a humanoid or beast that has a challenge rating no higher than its own, or back into her true form. It reverts to her true form if she dies. Any equipment she is wearing or carrying is absorbed or borne by the new form (Aleth's choice).

In a new form, Aleth retains her alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, and Intelligence, Wisdom, and Charisma scores, as well as this action. Its statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

Class Equivalence. Aleth holds skills and feats equivalent to a 17th level Warlock, and a 3rd level Fighter.

Aleth's Feats are Great Weapon Master, Savage Attacker, and Mage Slayer

Aleth's fighting style is Two-Weapon Fighting, and her Archetype is Battle Master. Her maneuver DC is 18, and her maneuvers are Parry, Lunging Attack, and Sweeping Attack. She can use Action Surge, but must take a long rest between uses.

Aleth's Pact Boon is the Pact of the Blade, with her chains serving as her Pact Weapon. Aleth has the following Eldritch Invocations: Lifedrinker, Thirsting Blade, Agonizing Blast, Eldritch Spear, Witch Sight, One with Shadows

Spellcasting. Aleth is a 17th level spellcaster, with five spell slots. Being a warlock, she casts all her spells at 5th level. Her spellcasting ability is Charisma, spell save DC is 21, and she has +13 to hit.

Cantrips (At will): eldritch blast, true strike

1st Level: cause fear, hex, armor of agathys, shield, wrathful smite

2nd Level: suggestion, hold person, phantasmal force, blur, branding smite

3rd Level: fireball, blink, elemental weapon, vampiric touch

4th Level: elemental bane, blight, phantasmal killer, staggering smite

5th Level: hold monster, dream, banishing smite, cone of cold

6th Level: investiture of ice

7th Level: finger of death

8th Level: power word: stun

9th Level: power word: kill

The wendigo can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Aleth regains spent legendary actions at the start of its turn.

Detect. Aleth makes a Wisdom (Perception) check.

Chain Lash. Aleth makes a melee attack with her chains.

Flit. Aleth disappears into smoke, moves up to 50ft from her original position, and reappears. This can be used in addition to her normal movement.