Demilich Mastermind

If the demilich makes a saving throw against an effect that deals half damage on a success, it takes no damage on a success and half damage on a failure.

If the demilich fails a saving throw, it can choose to succeed instead. When it does so, one of the five tiny warding gems set on its forehead or teeth shatters.

A demilich doesnt require air, sustenance, or sleep.

The demilich targets one creature within 120 feet forcing it to make a DC 17 Wisdom saving throw. On a success or if all the large soul gems on the demilichs skull are occupied the creature takes 40 necrotic damage and the demilich regains the same number of hit points. If the target fails its saving throw and there is at least one unoccupied soul gem on the demilichs skull the demilich regains 40 hit points and the target dies instantly. Its soul is trapped in a soul gem on the demilichs skull visible as a tiny creature-shaped mote of light. While its soul is trapped a creature can't be restored to life by any means. A soul that remains in a soul gem for 30 days is destroyed forever. If the demilich is defeated and a soul gem crushed the creature is restored to life if its body is within 100 miles. A creature that succeeds on a saving throw against this effect is immune to it for 24 hours.

The dust surrounding the demilich falls to the ground. The demilich and a nonmagical, unattended skull within 30 teleport, switching places. Until the demilich moves or attacks, it is indistinguishable from a nonmagical skull, and the dust composing the demilichs wraithlike body doesnt reform around it.

The dust of the demilichs body swirls in a 30-foot radius around the demilich. Each creature in the area makes a DC 17 Constitution saving throw. On a failure, the creature takes 21 (6d6) necrotic damage and is blinded until the end of its next turn. The demilich then moves up to its speed.

Each creature within 60 feet that can hear the demilich makes a DC 17 Wisdom saving throw. On a failure, a creature is frightened until the end of its next turn.

The demilich targets a Huge or smaller creature or an object weighing up to 1,000 pounds within 60 feet. If the target is a creature, it must succeed on a DC 17 Strength saving throw. Otherwise, the demilich moves the target up to 30 feet in any direction, including up. If another creature or object stops the targets movement, both take 10 (3d6) bludgeoning damage. At the end of this movement, the target falls if it is still in the air, taking falling damage as normal.

Only one legendary action can be used at a time and only at the end of another creatures turn. The demilich regains spent legendary actions at the start of its turn.