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

Strike of Revelation. When Ylxalol makes a melee attack with The Blade of the Undying King he uses his inteligence modifier in place of his strength for both attack and damage rolls

Tactical Wit. Ylxalol gains a bonus to his initiative rolls equal to his intelligence modifier.

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

Spellcasting. Ylxalol is a 20th-level spellcaster. his spellcasting ability is Intelligence with a +2 bonus from the Staff of Power, plus an additional +2 from the Black Robes of the Magi, plus an additional +3 from the Arcane Grimoire (spell save DC 25, +19 to hit with spell attacks). Ylxalol has the following wizard spells prepared:

Cantrips (at will): mage hand, fire bolt, ray of frost, mind sliver, shocking grasp

1st level (4 slots): charm person, magic missile, shield, chromatic orb

2nd level (3 slots): arcane lock, mind spike, shadow blade, mirror image

3rd level (3 slots): erupting earth, counterspell, dispel magic

4th level (3 slots): blight, dimension door, banishment

5th level (3 slots): synaptic static, telekinesis, wall of force

6th level (1 slot): disintegrate, contingency

7th level (1 slot): finger of death, power word pain

8th level (1 slot): abi-dalzim’s horrid wilting, power word stun

9th level (1 slot): power word kill, meteor swarm

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

Staff Of Power Spells. While holding this staff, Ylxalol can use an action to expend 1 or more of its charges to cast one of the following spells from it, using his spell save DC and spell attack bonus: cone of cold (5 charges), fireball (5th-level version, 5 charges), globe of invulnerability (6 charges), hold monster (5 charges), levitate (2 charges), lightning bolt (5th-level version, 5 charges), magic missile (1 charge), ray of enfeeblement (1 charge), or wall of force (5 charges).

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.

Blade of The Undying King. Melee Attack: +15 to hit, reach 5ft., one creature. Hit: 9 (1d8+6), or 11 (1d10+6) if wielded with 2 hands. When Ylxalol hits a creature they must make a DC 18 Intelligence saving throw. On a failed save the target take 12 (4d6) psychic damage and is stunned until the end of its next turn. On a success the target takes half as much damage and isn't stunned.

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

Cantrip. Ylxalol casts a cantrip.

Paralyzing Touch (Costs 2 Actions). Ylxalol uses its Paralyzing Touch.

Frightening Gaze (Costs 2 Actions). Ylxalol fixes his gaze on one creature he can see within 10 feet of him. 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 Ylxalol’s gaze for the next 24 hours.

Disrupt Life (Costs 3 Actions). Each non-undead creature within 20 feet of Ylxalol 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.