Avoidance. If the demilich is subjected to an effect that allows it to make a saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.
Legendary Resistance (3/day). If the demilich fails a saving throw, it can choose to succeed instead.
Maneuvers. The demilich uses maneuvers (maneuver save Difficulty 19). It has 35 stamina dice which are d8s, a dice limit of 6, regains all expended stamina dice when it finishes a long rest, and regains half its total stamina dice when it finishes a short rest. It knows the following maneuvers:
Turn Immunity. The demilich is immune to effects that turn undead.
Howl (Recharge 5–6). The demilich emits a bloodcurdling howl. Each creature within 5 meters of the demilich that can hear the howl must succeed on a Difficulty 14 Fortitude saving throw or drop to 0 health. On a success, the creature is frightened until the end of its next turn.
Life Drain (1/turn). The demilich targets up to three creatures that it can see within 2 meters of it. Each creature must succeed on a Difficulty 19 Fortitude saving throw or take 90 (20d8) necrotic damage, and the demilich regains health equal to the total damage dealt to all targets.
Legendary actions (3)
Only one legendary option can be used at a time and only at the end of another creature’s turn. The demilich regains spent legendary actions at the start of its turn.
Cloud of Dust. The demilich magically swirls its dusty remains. Each creature within 2 meters of the demilich, including around a corner, must succeed on a Difficulty 14 Fortitude saving throw or be blinded until the end of the demilich’s next turn. A creature that succeeds on the saving throw is immune to this effect until the end of the demilich’s next turn.
Energy Drain (Costs 2 actions). Each creature within 5 meters of the demilich must make a Difficulty 14 Fortitude saving throw. On a failure, the creature’s maximum health is magically reduced by 10 (3d6). If a creature’s maximum health is reduced to 0 by this effect, the creature dies. A creature’s maximum health can be restored with the restoration spell augmented to greater restoration or similar magic.
Flight. The demilich flies up to half its flying speed.
Vile Curse (Costs 3 actions). The demilich targets one creature it can see within 5 meters of it. The target must succeed on a Difficulty 14 Will saving throw or be magically cursed. Until the curse ends, the target has disadvantage on skill checks and saving throws. The target can repeat the saving throw at the end of each of its turns, ending the curse on a success.
On initiative count 20 (losing initiative ties), the demilich takes a lair action to cause one of the following effects; the same effect can’t be used two rounds in a row:
The demilich targets one creature it can see within 10 meters of it. An antimagic field fills the space of the target, moving with it until initiative count 20 on the next round.
The demilich targets any number of creatures it can see within 5 meters of it. No target can regain health until initiative count 20 on the next round.
The region containing the demilich’s lair is warped by the demilich’s magic, which creates one or more of the following effects:
The first time a non-evil creature enters the tomb’s area, the creature takes 16 (3d10) necrotic damage.
The tomb is warded against the magical travel of creatures the demilich hasn’t authorized. Such creatures can’t teleport into or out of the tomb’s area or use planar travel to enter or leave it. Effects that allow teleportation or planar travel work within the tomb as long as they aren’t used to leave or enter the tomb’s area.
If the demilich is destroyed, these effects fade over the course of 10 days.
As a reaction, which you use when an enemy moves within 1 meter of you, you can move up to half your speed without provoking opportunity attacks.
As a reaction, which you use when you make a skill check using Strength, Dexterity, or Constitution or you make a Fortitude or Reflex saving throw, you can focus your mind to overcome your body’s limitations. You make the roll with advantage. You can do so after the roll but before any effects of the roll occur.
As a reaction, which you use when you are hit by a weapon attack and take bludgeoning, piercing, or slashing damage from it, you halve the attack’s damage against you.
As a reaction, which you use when you are hit by an attack or missed by 4 or less that you can see or when you make a Reflex saving throw, you spin gracefully away, avoiding the swing or effect. You make the roll with advantage or the attack against you is made with disadvantage. You can do so after the roll but before any effects of the roll occur.