The lich is an 18th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 20, 1d20+12 to hit with spell attacks). The lich has the following wizard spells prepared:
Cantrips (at will): mage hand, prestidigitation, ray of frost
1st level (4 slots): detect magic, magic missile, shield, thunderwave
2nd level (3 slots): detect thoughts, invisibility, Melf's acid arrow, mirror image
3rd level (3 slots): animate dead, counterspell, dispel magic, fireball
4th level (3 slots): blight, dimension door
5th level (3 slots): cloudkill, scrying
6th level (1 slot): disintegrate, globe of invulnerability
7th level (1 slot): finger of death, plane shift
8th level (1 slot): dominate monster, power word stun
9th level (1 slot): power word kill
Legendary Resistance (3/Day). If the lich fails a saving throw, it can choose to succeed instead.
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.
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.
Lich can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Lich regains spent legendary actions at the start of its turn.
Cantrip. The lich casts a cantrip.
Paralyzing Touch (Costs 2 Actions).The lich uses its Paralyzing Touch.
Frightening Gaze (Costs 2 Actions).The lich fixes its gaze on one creature it can see within 10 feet of it. The target must succeed on a DC 18 Wisdom saving throw against this magic or become frightened for 1 minute. The frightened target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to the lich's gaze for the next 24 hours.
Disrupt Life (Costs 3 Actions). 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.