Legendary Resistance (3/Day). If the lich fails a saving throw, it can choose to succeed instead.

Arcane Sense. The lich can sense the presence and school of any arcane magic within 60 feet as a faint aura around any creature or object that bears magic. This ability can be blocked by a thin sheet of lead.

Rejuvenation. If it has a phylactery, a destroyed lich gains a new body in 1d10 days, regaining all its hit points and becoming active again. The new body appears within 5 feet of the phylactery.

Spellcasting. The lich is an 18th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 20, +12 to hit with spell attacks).

Turn Resistance. The lich has advantage on saving throws against any effect that turns undead.

Paralyzing Touch. Melee Spell Attack: +12 to hit, reach 5 ft., one creature. Hit: 10 (3d6) cold damage. The target must succeed on a DC 18 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Dominate Monster (1/day). 

Cloud of Death. The lich creates a 10 foot radius sphere of toxic yellow-green fog centered on a point it can see within 120 feet. The cloud lasts for 10 minutes or until strong wind disperses it. Its area is heavily obscured. When a creature enters the spell's area for the first time on a turn or starts its turn there, that creature must make a DC 20 Constitution saving throw. The creature takes 22 (5d8) poison damage on a failed save, or half as much damage on a successful one. Creatures are affected even if they hold their breath or don't need to breathe.

Detect Thoughts (2nd-level). 

Dimension Door (4th-level). 

Acid Arrow. Ranged Spell Attack: +12 to hit, range 90 ft., one target. Hit: 10 (4d4) acid damage plus an additional 5 (2d4) acid damage at the end of its next turn. Miss: 5 (2d4) acid damage.

Lifeforce Tether (Recharge 5-6). Ranged Spell Attack: +12 to hit, range 30 ft., one creature. Hit: Whenever the lich takes damage, it takes half the damage (rounded down), and the target takes the remaining damage. This spell lasts one minute, until the target has full cover from the lich, or until the lich loses concentration.

Open Grave. The lich creates one zombie or skeleton under its control in an unoccupied space within 60 feet. Any non-undead creature within 5 feet of the selected space must make a DC 20 Constitution saving throw, taking 9 (2d8) necrotic damage on a failure or half as much on a success. The lich can have a maximum of 20 creatures under its control from this spell.

Disdain. The lich makes one Paralyzing Touch attack against one creature when it enters a space within 5 feet of the lich.

Shatterspell. When a target within 60 feet of the lich casts a spell, the lich can use a reaction to cast counterspell as a 3rd-level spell. If this causes the target spell to fail, the caster takes 5 (1d10) force damage plus 5 (1d10) force damage for each level of the spell intercepted.

Vile Shroud. When it is the target of an attack or magic missile, the lich can cast shield. Any creature within 5 feet of the lich must make a DC 20 Strength saving throw, taking 10 (3d6) poison damage plus 7 (2d6) necrotic damage and being pushed 10 feet away on a failure. On a success, a target takes half as much damage and is not pushed.

 VILLAIN ACTIONS: 

1. Disrupt Life. Each non-undead creature within 20 feet of the lich must make a DC 18 Constitution saving throw against this magic, taking 21 (6d6) necrotic damage on a failed save, or half as much damage on a successful one. Any concentration save imposed by this spell automatically fails.

2. Mortifying Gaze. Each creature of the lich's choice within a 50 foot cone must succeed on a DC 18 Wisdom saving throw against this magic or become frightened for 1 minute. While this effect persists, an affected creature takes 9 (2d8) psychic damage at the start of each turn. A target that fails this saving throw can repeat it at the end of each of its turns, ending the effect on itself on a success.

3. Crush Lifeforce. A target creature within 60 feet must make a DC 20 Constitution saving throw, taking necrotic damage equal to its missing hit points on a failure or half as much on a success. A humanoid reduced to 0 hit points by this spell is killed and rises again at the start of the lich’s next turn as a zombie that is permanently under the lich’s command.