Negative Energy Cone.

The death tyrant's central eye emits an invisible, magical 150-foot cone of negative energy. At the start of each of its turns, the tyrant decides which way the cone faces and whether the cone is active.

Any creature in that area can't regain hit points. Any humanoid that dies there becomes a zombie under the tyrant's command. The dead humanoid retains its place in the initiative order and animates at the start of its next turn, provided that its body hasn't been completely destroyed.

Actions

Bite.

Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 14 (4d6) piercing damage.

Eye Rays.

The death tyrant shoots three of the following magical eye rays at random (reroll duplicates), choosing one to three targets it can see within 120 feet of it:

1. Charm Ray. The targeted creature must succeed on a DC 17 Wisdom saving throw or be charmed by the death tyrant for 1 hour, or until the death tyrant harms the creature.
2. Paralyzing Ray. The targeted creature must succeed on a DC 17 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.
3. Fear Ray. The targeted creature must succeed on a DC 17 Wisdom saving throw or be frightened 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.
4. Slowing Ray. The targeted creature must succeed on a DC 17 Dexterity saving throw. On a failed save, the target's speed is halved for 1 minute. In addition, the creature can't take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
5. Enervation Ray. The targeted creature must make a DC 17 Constitution saving throw, taking 36 (8d8) necrotic damage on a failed save, or half as much damage on a successful one.
6. Telekinetic Ray. If the target is a creature, it must succeed on a DC 17 Strength saving throw or the death tyrant moves it up to 30 feet in any direction. It is restrained by the ray's telekinetic grip until the start of the death tyrant's next turn or until the death tyrant is incapacitated.If the target is an object weighing 300 pounds or less that isn't being worn or carried, it is moved up to 30 feet in any direction. The death tyrant can also exert fine control on objects with this ray, such as manipulating a simple tool or opening a door or a container.
7. Sleep Ray. The targeted creature must succeed on a DC 17 Wisdom saving throw or fall asleep and remain unconscious for 1 minute. The target awakens if it takes damage or another creature takes an action to wake it. This ray has no effect on constructs and undead.
8. Petrification Ray. The targeted creature must make a DC 17 Dexterity saving throw. On a failed save, the creature begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the creature is petrified until freed by the greater restoration spell or other magic.
9. Disintegration Ray. If the target is a creature, it must succeed on a DC 17 Dexterity saving throw or take 45 (10d8) force damage. If this damage reduces the creature to 0 hit points, its body becomes a pile of fine gray dust.If the target is a Large or smaller nonmagical object or creation of magical force, it is disintegrated without a saving throw. If the target is a Huge or larger object or creation of magical force, this ray disintegrates a 10-foot cube of it.
10. Death Ray. The targeted creature must succeed on a DC 17 Dexterity saving throw or take 55 (10d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.

Legendary Actions

The death tyrant 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. The death tyrant regains spent legendary actions at the start of its turn.

Eye Ray. The death tyrant uses one random eye ray.

Lair Actions

When fighting inside its lair, a death tyrant can invoke the ambient magic to take lair actions. On initiative count 20 (losing initiative ties), the death tyrant can take one lair action to cause one of the following effects:

An area that is a 50-foot cube within 120 feet of the tyrant is filled with spectral eyes and tentacles. To creatures other than the death tyrant, that area is lightly obscured and difficult terrain until initiative count 20 on the next round.
Walls sprout spectral appendages until initiative count 20 on the round after next. Any creature, including one on the Ethereal Plane, that is hostile to the tyrant and starts its turn within 10 feet of a wall must succeed on a DC 17 Dexterity saving throw or be grappled. Escaping requires a successful DC 17 Strength (Athletics) or Dexterity (Acrobatics) check.
A spectral eye opens in the air at a point within 50 feet of the tyrant. One random eye ray of the tyrant shoots from that eye, which is considered to be an ethereal source, at a target of the tyrant's choice. The eye then closes and disappears.

The death tyrant can't repeat an effect until all three have been used, and it can't use the same effect on consecutive rounds.

Regional Effects

A region containing a death tyrant's lair is warped by the creature's unnatural presence, which creates one or more of the following effects:

Creatures within 1 mile of the tyrant's lair sometimes feel as if they're being watched even when they aren't.
When a creature hostile to the tyrant and aware of its existence finishes a long rest within 1 mile of the tyrant's lair, roll a d20 for that creature. On a roll of 10 or lower, the creature is subjected to one random eye ray of the tyrant.

If the death tyrant dies, these effects fade over the course of 1d10 days.

Environment: Underdark

Death Tyrant