Auril the Frostmaiden

Divine Being: Auril can’t be surprised and can’t be changed into another form against her will.

Divine Resurrection:  When Auril drops to 0 hit points, her crystalline form shatters and her divine spark vanishes. She is dead until the next winter solstice, when she reappears at full health in a cold, remote location of her choosing.

Innate Spellcasting: Auril’s innate spellcasting ability is Charisma (spell save DC 21, +13 to hit with spell attacks). She can innately cast the following spells, requiring no material components:

At will: chromatic orb (cold orb only), detect magic, misty step

2/day each: control weather, detect thoughts, ice storm

Legendary Resistance (5/Day): If Auril fails a saving throw, she can choose to reroll the save and take the new roll.

Magic Resistance: Auril has advantage on saving throws against spells and other magical effects.

Unusual Nature: Auril doesn’t require air, food, drink, or sleep.

Frigid Aura: So long as Auril has at least 1 hit point, each creature within 10 feet of her takes 10 cold damage at the start of each of her turns.

Ice Core: Aurils form is held together by the Crystal in her Chest which has immunity to all damage types except celestial piercing.

The Crystal has a total of 3 Hitpoints and grats Auril 175 Temporary Hitpoints. Once all those Temporary Hitpoints are expended she becomes stunned until the Start of her Next Turn and some Iceicles from her Body break off creating 1 Celestial Ice Spear.

This Spear can be thrown at Aurils Core. To hit it one must succeed a DC 21 Abilitycheck with ones highest Abilityscore + their proficenciemodifier.

The Spear is Cold to the Touch and wants to absorb the Warmth and life energy of whoever touches the Spear. The one throwing the Spear can choose to take 1d6 to 10d6 cold damage gaining a +1 to their Ability Check for every D6 of damage taken to a maximum of +5 and if one chooses to take all 10d6 Cold damage they gain Advantage on their Abilitycheck. This Damage can't be reduced in any way.

Once a Spear succesfully hits the Core it deals 1 Celestial piercing damage.

At the Start of Aurils Turn after all her Temporary Hitpoints were reduced to 0 her core grants her another 175 Temporary Hitpoints.

When the Core reaches 0 Hitpoints Auril dies.

Multiattack. Auril uses Touch of Frost or Polar Ray twice.

Touch of Frost. Melee SpellAttack: +13 to hit, reach 10 ft., 1 target. Hit: 13 (3d8) [cold] damage. 

Polar Ray. Ranged Spell Attack: +13 to hit, range 120ft., 1 target. Hit: 14 (4d6) [cold] damage.

Cone of Cold (Recharges after a Short or Long Rest). Auril causes a magical blast of cold air to erupt from her hand. Each creature in a 60-foot cone must make a DC 21 Constitution saving throw, taking 36 (8d8) cold damage on a failed save, or half as much damage on a successful one.

Create Ice Mephit (3/Day). Auril breaks off an icicle from her body and hurls it into an unoccupied space she can see within 20 feet of her, where it magically transforms into an ice mephit. The mephit acts immediately after Auril in the initiative order and obeys her commands.

Ice Stasis (Recharge 5–6). Auril magically creates a gem-sized ice crystal that hovers in a space within 5 feet of her. Auril then targets a creature she can see within 60 feet of the crystal. The target must succeed on a DC 21 Charisma saving throw or become trapped in the crystal, which is immovable. If the saving throw succeeds, the crystal shatters and nothing else happens. A creature trapped in the crystal is stunned, has total cover against attacks and other effects outside the crystal, and takes 21 (6d6) cold damage at the start of each of its turns. The creature can repeat the saving throw at the end of each of its turns, freeing itself on a success. The creature is also freed if the crystal is destroyed, which is a Tiny object with AC 18, 9 hit points, and immunity to all damage except fire damage. The freed creature appears in an unoccupied space of its choice within 30 feet of the shattered crystal.

Blizzard Veil. Auril creates a magical blizzard in a 30-foot-radius sphere centered on herself. The area within the sphere is heavily obscured, and the sphere moves with Auril. The effect lasts until Auril drops to 0 hit points in this form, until she chooses to end the effect (no action required), or until her concentration is broken (as if concentrating on a spell).

Attack. Auril makes one attack with either Polar Ray or Touch of Frost.

Intensify Aura (Costs 2 Actions). Auril’s Frigid Aura deals an extra 10 cold damage until the end of her next turn.

Blinding Gleam (Costs 2 Actions). Auril’s form flares with a blue light. Each creature that can see Auril and is within 10 feet of her must succeed on a DC 17 Wisdom saving throw or be blinded by Auril’s magical gleam for 1 minute. The blinded creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Ice Flurry (Costs 2 Actions). Each creature within 30 feet of Auril takes 5 (2d4) piercing damage from swirling ice, and nonmagical, open flames in that area are extinguished.

Splinter (Costs 3 Actions). Auril uses Create Ice Mephit or causes one to ice mephit she can see within 60 feet of her to explode and die. A mephit that dies in this way does not use its Death Burst. Instead, each creature within 10 feet of the exploding mephit must succeed on a DC 21 Dexterity saving throw, taking 13 (3d8) piercing damage on a failed saving throw, and half as much damage on a successful one.