Amalthea, Goddess of the Moon and Shadows

Queen of Shadow. When dropped to 0 hp, Amalthea instead drops to 100 hp and gains access to her mythical abilities.

Inescapable Destruction. Necrotic and Cold damage dealt by Amalthea ignores resistance and treats immunity as resistance.     

limited Magical Immunity. Unless Almalthea wishes to be affected by it, spells 4th level or lower have no affect on her. 

Darkness. Amalthea magically sheds darkness in a 15-foot radius.

Magic Weapon. Amalthea's attacks are considered magical. 

Innate Spellcasting. Amalthea, being a powerful Goddess, is an innate spellcaster, being able to cast the following spells without any need for material components. (Spell save 23, plus 15 to hit) 

At Will. detect evil and good, dispel magic (up to 5th level), evard's black tentacles, chill touch, shadow blade (up to 5th level), umbral tendril (up to 5th level), swallow magic, moonbeam up to 4th level, scorching ray (up to 5th level) 

3 times a day. blight, vampiric touch (up to 5th level), contagion, enervation, counterspell (up to 5th level), major image (up to 4th level), dream, fount of moonlight, 

1 time a day. alustriel's mooncloak, crown of stars up to 8th level, prismatic spray, maddening darkness, mental prison

Multi Attack: When using shadow blade, Amalthea can attack up to two times. 

Sneak Attack. Retaining some of her mortal abilities when she was a rouge, Amalthea still remembers how to attack someone in the best possible way when she has the advantage on them. When she makes any kind of melee attack with advantage once per turn, she can add 8d6 of the damage type the weapon does to the creature she attacks. 

Teleport. Amalthea can teleport up to 60 ft. She appears to be wrapped in shadow before disappearing. 

Hardened Shadow. Amalthea can pull shadow around her to boost her AC, increasing it by 3 till the start of her next turn. She can do this 2 times a day. 

Shadowy Embrace. When subject to an attack of any kind, Amalthea can wrap herself in shadow, adding 5 to her AC and making magic attacks like Magic Missile unable to hit her. 

Attack of Opportunity. When someone leaves Amalthea's attack range, instead of melee attacking them, she can instead cast any spell that takes only an action and is instantaneous.  

Amalthea 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. Amalthea regains spent legendary actions at the start of its turn.

Teleport. Amalthea can teleport 30 ft. 

Movement. Amalthea can move up to half her movement without incurring attack of opportunity.

Hardened Shadow (Costs 2 actions). Regains a use of hardened shadow. 

Magic (Cost 2 actions). Amalthea can cast a spell, granted it takes one action and is instantaneous 

Magical Reserves (Cost 3 actions). Regain a use of counter spell

Queen of Shadow. Upon almost being killed, Amalthea briefly becomes one with Shadow and darkness. She gains an additional legendary action point, unlocks new abilities, and gains access to Mythical Actions. After one hour, her magical reserves runs out, losing access to this form and gaining 4 levels of exhaustion. If she does not rest within the hour after losing this form, she gains another level of exhaustion. 

Immunity. Amalthea gains immunity to Necrotic damage. 

Regeneration. Amalthea regenerates 20 hp at the start of her turns, but with this regeneration she can't be healed past 100 HP.

True Master. Cirrus can now concentrate on 2 spells, and can cast two spells per action, but only one can be a concentration spell. 

One With Shadow (Costs 3 actions). Amalthea merges with darkness, her physical form disappearing. While in this form, she becomes incorporeal, unable to be targeted by any melee, ranged, or spell attack. AOE spells, like fireball, do only half damage, and she is able to make DEX saving throws with advantage. Upon a success, she takes no damage. She can move freely up to 60 feet, and remain in this form for up to half a minute. She can not make any attacks, cast any spells, or in any way interact with anything outside of her incorporeal form. She can benefit from friendly healing spells.

Enraged Shadow (Cost 4 actions). While in her incorporeal form, she can make Shadows and darkness take physical shape. She can move into a creature's space and force them to make a DEX or STR saving throw (DC 25). On a failure, the creature becomes incapacitated, restrained, and blinded, taking 6d8 narcotic and 6d8 cold damage. The effected creature can remake the saving throw at the start of their turn. The creature keeps the conditions and keeps taking the damage until after they have escaped. The creature can either make the save to escape, or an ally can physically move them out of the shadowy embrace.