Undead Fortitude. If damage reduces Abaderzum to 0 hit points, it must make a Constitution saving throw with a DC equal the damage taken minus 10, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Antimagic Cone. The beholder's central eye creates an area of antimagic, as in the antimagic field spell, in a 150-foot cone. At the start of each of its turns, the beholder decides which way the cone faces and whether the cone is active. The area works against the beholder's own eye rays.

Negative Energy Cone. The beholders 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.

Spellcasting. [Abaderzum] is a 20th level spellcaster. Its spellcasting ability is [charisma] (spell save DC 28, +20 to hit with spell attacks). [Abaderzum] has following [wizard] spells prepared:
Cantrips (at will): [spell name], [spell name] 
1st level (# slots): [spell name], [spell name] 

bite. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit: 27 (6d6 + 3) [piercing] damage. 

Eye Ray. Abederzum shoots three of the following magical eye rays at random (reroll duplicates), choosing one to three targets it can see within 120 ft. of it:

1. Charm Ray. The targeted creature must succeed on a DC 25 Wisdom saving throw or be charmed by Abaderzum for 1 hour, or until Abaderzum harms the creature.

2. Paralyzing Ray. The targeted creature must succeed on a DC 25 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 25 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 25 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 25 Constitution saving throw, taking 54 (12d8) 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 25 Strength saving throw or Abaderzum moves it up to 60 ft. in any direction. It is restrained by the ray’s telekinetic grip until the start of Abaderzum's next turn.

   If the target is an object weighing 450 pounds or less that isn’t being worn or carried, it is moved up to 40 ft. in any direction. Abaderzum 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 25 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 25 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 25 Dexterity saving throw or take 68 (15d8) 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 20-foot cube of it.

10. Death Ray. The targeted creature must succeed on a DC 25 Dexterity saving throw or take 83 (15d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.

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

Eye Ray. Abaderzum uses one random eye ray.