Valaketh

Legendary Resistance (3/Day, or 4/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.

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

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

Multiattack. The dragon makes three Rend attacks. It can replace one attack with a use of Spellcasting to cast Melf’s Acid Arrow (level 3 version).

Rend. Melee Attack Roll: +12, reach 10 ft. Hit: 13 (2d6 + 7) Slashing damage plus 4 (1d8) Acid damage.

Acid Breath (Recharge 5–6). Dexterity Saving Throw: DC 19, each creature in a 60-foot-long, 5-foot-wide Line. Failure: 54 (13d8) Acid damage. Success: Half damage.

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 18, +10 to hit with spell attacks):

At Will: Detect Magic, Fear, Melf’s Acid Arrow (level 3 version)

1/Day Each: Speak with Dead, Vitriolic Sphere

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

Blight. Constitution Saving Throw: DC 18, one creature the dragon can see within 120 feet. Failure: 40 (8d8) Necrotic damage or half as much on a successful one. Failure or Success: The dragon can’t take this action again until the start of its next turn.

Terrifying Presence. Wisdom Saving Throw: DC 18, each creature in a 30-foot Emanation originating from the dracolich. Failure: 11 (2d10) Psychic damage, and the target has the Frightened condition until the end of its next turn. Failure or Success: The dracolich can’t take this action again until the start of its next turn.

Pounce. The dragon can move up to half its Speed, and it makes one Rend attack.