Magic Rings. Xanathar wears a ring of truth telling on its Reduce Ray eye-stalk, a ring of mind shielding on its Sleep Ray eye-stalk, a ring of force resistance on its Slowing Ray eye-stalk and a fragment of the Shade Seal forged by Gond hooked around its Rust Ray eye-stalk.

Living Shadow. While in dim light or darkness, the beholder has resistance to damage that isn’t force, psychic, or radiant.

Shadow Stealth. While in dim light or darkness, the beholder can take the Hide action as a bonus action.

Sunlight Sensitivity. While in sunlight, the beholder has disadvantage on attacks rolls, as well as on Wisdom (Perception) checks that rely on sight.

Antimagic Cone. Zushaxx'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, Zushaxx decides which way the cone faces and whether the cone is active. The area works against Zushaxx's own eye rays.

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

Eye Rays. Zushaxx shoots three of the following magical eye rays at random (re-roll duplicates), choosing one to three targets it can see within 120 feet of it:

1. Draining Ray. The targeted creature must succeed on a DC 17 Dexterity saving throw or take 18 (4d8) necrotic damage, and its Strength score is reduced by 1d4. The target dies if this reduces its Strength to 0. Otherwise, the reduction lasts until the target finishes a short or long rest. If a non-evil humanoid dies from this attack, a shadow rises from the corpse 1d4 hours later under the beholder’s control.
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. Reduce Ray. The targeted creature must make a DC 17 Constitution saving throw, on a failure the target is subjected to the effects of the Enlarge/Reduce spell, but only Reduces.
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. Energy Ray. The targeted creature must make a DC 17 Constitution saving throw, taking 36 (8d8) lightning 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. On a fail, Zushaxx moves it up to 30 feet in any direction. It is restrained by the ray’s telekinetic grip until the start of Zushaxx’s next turn or until the beholder 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. Zushaxx 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. Rust Ray. The targeted creature must succeed on a DC 17 Dexterity saving throw or receive a permanent -1 penalty to one piece of armor the creature is wearing, if it is made of metal. If the target isn't wearing metal armor then the ray affects the creature's weapon instead, reducing the damage of the weapon by -2. If the ray reduces the creature's armor to an AC of 10 or a shield to a +0 bonus, it is destroyed. If the ray reduces a weapon past 1d4 damage, it is destroyed. 
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.

Shadow Weave's Insight. When a creature makes an attack roll, ability check or saving throw, Zushaxx can pull from a pool of 20 shadow points and use up to the full amount of shadow points to reduce the creatures' roll. This ability can only be used once per round. After each round, roll a d6. On a 5 or 6, Zushaxx regains 10 shadow points.

Zushaxx can take 3 legendary actions, using the Eye Ray option below. It can take only one legendary action at a time and only at the end of another creature’s turn. Zushaxx regains spent legendary actions at the start of its turn.

Eye Ray. Zushaxx uses one random eye ray.