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.

Actions

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.

Legendary Actions

The cosmic horror 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 cosmic horror regains spent legendary actions at the start of its turn.

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.

Cosmic Horror