Boneskinner

Bright Light Sensitivity. While in bright light, the Boneskinner has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Unnatural Aura. A creature that starts its turn within 90 feet of the Boneskinner, and is in dim light or darkness, takes 4 (1d8) necrotic damage.

Devil's Sight. Magical darkness doesn't impede the Boneskinner's darkvision.

Regeneration. If the Boneskinner has at least 1 hit point, it regains 10 hit points at the start of its turn. If it starts its turn in bright light, this trait doesn’t function for this turn.

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

Hidden Step. If the Boneskinner is in dim light or darkness, it can, as a bonus action, turn invisible until the end of its next turn or until it attacks, makes a damage roll, or forces someone to make a saving throw.

Innate Spellcasting. The Boneskinner's innate spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks). It can innately cast the following spells, requiring no components:

At will: darkness, dispel magic, chill touch

1/day: cloudkill, dominate person, mass suggestion

Hearts of the Boneskinner (Mythic Trait; Recharges on a Short or Long Rest). When the Boneskinner is reduced to 0 hit points, it doesn’t die or fall unconscious. Instead, the damage creates cracks in its skin, revealing its hearts. The Boneskinner has two hearts, both in its chest, next to each other. A heart has an AC of 16 and 40 hit points. It is resistant to bludgeoning, piercing, and slashing damage from nonmagical attacks, and it is immune to all conditions. If it is forced to make a saving throw, treat its ability scores as 10 (+0). If the Boneskinner finishes a short or long rest, the skin heals, any destroyed hearts regenerate, and the hearts are covered again. The Boneskinner dies when both the hearts are destroyed.

Multiattack. The Boneskinner makes three attacks, one with its bite and two with its claws.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) piercing  damage plus 9 (2d8) necrotic damage.

Claw. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 9 (1d8 + 5) slashing damage.

Death Wind (Recharge 5-6). The Boneskinner emits a 40-foot cone of necrotic, poisonous gas. Every creature in the area must make a DC 16 Constitution saving throw, or take 18 (4d8) poison damage, 18 (4d8) necrotic damage, and are frightened. On a successful save, a creature takes half as much damage, and is not frightened. Any source of light caught in the cone, magical or otherwise, is extinguished.

Negate Spell (2/Day). When the Boneskinner sees a creature within 60 feet of it casting a spell, it tries to interrupt it. If the creature is casting a spell using a spell slot of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th-level or higher, it must succeed on a DC 16 Intelligence saving throw, or the spells fails and has no effect.

The Boneskinner 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. The Boneskinner regains spent legendary actions at the start of its turn.

Move. The Boneskinner moves up to its speed.

Claw. The Boneskinner makes one claw attack.

Scorned. The Boneskinner casts a spell from its Innate Spellcasting trait.

If the Boneskinner's mythic trait is active, it can use the options below as legendary actions:

Curse. The Boneskinner attempts to curse a creature it can see within 30 feet of it. The target must make a DC 16 Wisdom saving throw, or suffer vulnerability to necrotic damage until the end of the Boneskinner's next turn.

Rampage. The Boneskinner makes two attacks: one with its bite and one with its claw.