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.
Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 14 (4d6) piercing damage.
Eye Rays. The beholder 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:
Bite. : Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 14 (4d6) piercing damage.
When fighting inside its lair, a beholder can invoke the ambient magic to take lair actions. On initiative count 20 (losing initiative ties), the beholder can take one lair action to cause one of the following effects:
A 50-foot-square area of ground within 120 feet of the beholder becomes slimy; that area is difficult terrain until initiative count 20 on the next round.
Walls within 120 feet of the beholder sprout grasping appendages until initiative count 20 on the round after next. Each creature of the beholder's choice that starts its turn within 10 feet of such a wall must succeed on a DC 15 Dexterity saving throw or be grappled. Escaping requires a successful DC 15 Strength (Athletics) or Dexterity (Acrobatics) check.
An eye opens on a solid surface within 60 feet of the beholder. One random eye ray of the beholder shoots from that eye at a target of the beholder's choice that it can see. The eye then closes and disappears.
The beholder can't repeat an effect until they have all been used, and it can't use the same effect two rounds in a row.
A region containing a beholder'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 beholder's lair sometimes feel as if they're being watched when they aren't.
When the beholder sleeps, minor warps in reality occur within 1 mile of its lair and then vanish 24 hours later. Marks on cave walls might change subtly, an eerie trinket might appear where none existed before, harmless slime might coat a statue, and so on. These effects apply only to natural surfaces and to nonmagical objects that aren't on anyone's person.
If the beholder dies, these effects fade over the course of 1d10 days.