Colwin of the Cold Oblivion

Winter Storm. Colwin is surrounded by a 10ft emanation of intense frost. Any creature that starts its turn within the emanation takes (1d6) cold damage. Creatures that end their turn within the emanation must make a DC 16 Constitution saving throw or have disadvantage on attack rolls and saving throws until the end of their next turn.

Legendary Resistance (2/Day). If Colwin fails a saving throw, he can choose to succeed instead.

Multiattack. Colwin makes two Icy Slam or Chilled Spike attacks in any combination.

Icy Slam. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 2d10 bludgeoning damage plus 2d6 cold damage.

Chilled Spike. Ranged Weapon Attack: +11 to hit, range 60 ft., one target. Hit: 1d10 bludgeoning damage plus 1d6 cold damage.

Frozen Roots (Recharge 5-6). Colwin summons a mass of icy roots that erupt from the ground in a 20-foot radius centered on a point within 30 feet. Each creature in the area must make a DC 19 Strength saving throw or be restrained for 1 minute. A restrained creature can use its action to shatter the roots, ending the effect on itself.

Spellcasting. Colwin casts one of the following spells, using Wisdom as the spellcasting ability (spell save DC 16, +8 to hit with spell attacks):

At Will: ray of frost (level 11 version), thaumaturgy, frostbite (level 11 version)
2/Day Each: ice knife (level 3 version), fog cloud (level 3 version)
1/Day Each: ice storm (level 4 version)

Embrace The Cold. As a bonus action, Colwin can use his connection to the cold to regenerate 15 hit points at the start of his turn if he has at least 1 hit point remaining. This regeneration can be interrupted if Colwin is subject to fire damage.

Frostbitten Vengeance. When a creature hits Colwin with a melee attack, he can use its reaction to deal (1d8) cold damage and (1d8) bludgeoning damage to the attacker and reduce their speed by 10 feet until the start of their next turn.

Colwin 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. Colwin regains spent legendary actions at the start of his turn.

Channelling Frost. Colwin may use Spellcasting to cast one spell.

Icy Mirage. Colwin can move up to his movement speed without provoking opportunity attacks.

Chilling Grasp. Colwin targets one creature within 60 feet. The target must make a DC 16 Constitution saving throw or take (3d6) cold damage and have their movement speed reduced by half on a failure. Half damage and no speed reduction on a save.