Legendary Resistance (3/day). If Acheron fails a saving throw, she can choose to succeed instead.

Magic Resistance. Acheron has advantage against spells and other magical effects.

Emanator of Nihility (1/day). When Acheron falls below 120 hit points, she uses her reaction to cast the ravenous void spell to a point behind her. This spell requires no spell components or concentration and Acheron is immune to its effects.

While the spell is in effect, Acheron gains 25 temporary hit points at the start of her turn and any lightning damage she deals becomes force damage instead.

Multiattack. Acheron makes two attacks with Naught.

Naught (Greatsword). Melee Weapon Attack: +16 to hit, reach 5 ft., 1 target. Hit: 15 (1d10 + 10) slashing damage plus 12 (3d8) lightning damage.

Innate Spellcasting. Acheron casts lightning bolt or chain lightning without spell components (Spell Save DC 19).

Teleport. Acheron magically teleports to an unoccupied space within 30 feet of her.

Acheron 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. Acheron regains spent legendary actions at the start of her turn.

Attack. Acheron makes an attack with Naught.

Move. Acheron moves up to half her speed without provoking opportunity attacks.

Spellcasting (Costs 2 Actions). Acheron uses her Innate Spellcasting.