Armor Class 15 (natural armor)
Hit Points 280 (16d20 + 112)
Speed 50 ft., fly 100 ft.
Saving Throws INT +13, WIS +8, CHA +13
Damage Immunities acid, poison
Condition Immunities charmed, frightened, poisoned
Senses darkvision 240 ft., passive Perception 12
Languages Deep Speech, telepathy 240 ft.
Challenge 18
Legendary Resistance (3/Day). If the horror fails a saving throw, it can choose to succeed instead.
Unusual Nature. The horror doesn't require air.
Multiattack. The horror makes one Bite attack and two Tentacle attacks.
Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 22 (4d6 + 8) piercing damage.
Tentacle. Melee Weapon Attack: +14 to hit, reach 30 ft., one target. Hit: 18 (3d6 + 8) force damage, and if the target is a creature, it is grappled (escape DC 18). Until this grapple ends, the horror can't use this tentacle against other targets. The horror has 1d8 + 1 tentacles, each of which can grapple one target.
Psychic Whispers (Recharge 5–6). The horror emits dreadful whispers in a 60-foot-radius sphere centered on itself. Each creature in the sphere that isn't an Aberration must make a DC 21 Wisdom saving throw, taking 33 (6d10) psychic damage on a failed save, or half as much damage on a successful one.
Crushing Tentacle. The horror crushes one creature it is grappling. The grappled creature must make a DC 22 Constitution saving throw, taking 18 (3d6 + 8) force damage on a failed save, or half as much damage on a successful one.
Poison Jet (Costs 2 Actions). Foul gas squirts from the horror in a 30-foot line that is 5 feet wide. Each creature in the line must succeed on a DC 21 Constitution saving throw or take 14 (4d6) poison damage.
Teleport (Costs 2 Actions). The horror teleports, along with any creatures it is grappling, to an unoccupied space it can see within 120 feet of itself.
BAM, p. 18