Blue Dracolich Mage

Legendary Resistance (4/Day, or 5/Day in Lair). If the dracolich fails a saving throw, it can choose to succeed instead.

Life Suppression. Creatures within 60 feet of the dracolich can’t regain Hit Points.

Magic Resistance. The dracolich has Advantage on saving throws against spells and other magical effects.

Soul Gem. The dracolich has a magical gem. If it is destroyed while the gem is on the same plane of existence as it, the dracolich gains a new body in 1d20 days, regaining all its Hit Points and appearing within 5 feet of the gem.

The gem is a Tiny object that has AC 20; HP 85; and Immunity to Lightning, Necrotic, Poison, and Psychic damage. The gem regains all its Hit Points at the end of every turn, but it turns to dust if reduced to 0 Hit Points. If the gem is destroyed, the dracolich can create a new one by completing an 8-hour ritual using a gem worth 1,000+ GP and by expending 5,000 GP, which the ritual consumes.

Multiattack. The dracolich makes three Arcane Burst or Rend attacks in any combination. It can replace one attack with a use of Spellcasting to cast (A) Ray of Sickness (level 3 version) or (B) Shatter (level 3 version).

Arcane Burst. Melee or Ranged Attack Roll: reach 5 ft., or range 120 ft. Hit: 26 (4d10 + 4) Force damage.

Rend. Melee Attack Roll: +15, reach 15 ft. Hit: 17 (2d8 + 8) Slashing damage plus 5 (1d10) Lightning damage and 4 (1d8) Necrotic damage.

Breath Weapon (Recharge 5–6). The dracolich uses one of the following breath weapons:

Lightning Breath. Dexterity Saving Throw: DC 22, each creature in a 90-foot-long, 10-foot-wide Line. Failure: 66 (12d10) Lightning damage. Success: Half damage.
Necrotic Breath. Constitution Saving Throw: DC 22, each creature in a 75-foot Cone. Failure: 65 (10d12) Necrotic damage. Success: Half damage.

Spellcasting. The dracolich casts one of the following spells, requiring no Material components and using Intelligence as the spellcasting ability (spell save DC 19, +11 to hit with spell attacks):

At Will: Alarm, Detect Magic, Identify, Invisibility, Mage Hand, Ray of Sickness (level 3 version), Sending, Shatter (level 3 version), Slow, Unseen Servant
1/Day Each: Antimagic Field, Chain Lightning, Command (level 6 version), Create Undead (level 8 version), Finger of Death, Project Image, Scrying, Teleport

Shape-Shift. The dracolich shape-shifts into a Gargantuan or smaller Beast, Dragon, Giant, or Humanoid, or it returns to its true draconic form. The dracolich's game statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. This effect ends early if the dracolich is reduced to 0 Hit Points.

Terrifying Counterspell. The dracolich casts Counterspell in response to the spell’s trigger, using the same spellcasting ability as Spellcasting. If the target fails its saving throw, it takes 11 (2d10) Psychic damage, and has the Frightened condition until the end of its next turn.

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, the dracolich can expend a use to take one of the following actions. The dracolich regains all expended uses at the start of each of its turns.

Cloaked Flight. The dracolich uses Spellcasting to cast Invisibility on itself, and it can fly up to half its Fly Speed. The dracolich can’t take this action again until the start of its next turn.

Induce Lethargy. The dracolich uses Spellcasting to cast  Slow. The dracolich can’t take this action again until the start of its next turn.

Tail Swipe. The dracolich makes one Rend attack.