Traits

Eldritch Anatomy. The Voidspawn Behemoth can squeeze through spaces as though it were a Medium creature, and it has advantage on checks and saves against being grappled or restrained.

Aura of Madness. Any creature that starts its turn within 30 feet of the Behemoth must succeed on a DC 19 Wisdom saving throw or be affected by short-term madness (roll on the Madness table in the DMG) for 1 minute. The creature can repeat the save at the end of each of its turns.

Legendary Resistance (3/Day). If the Behemoth fails a saving throw, it can choose to succeed instead.

Magic Resistance. The Behemoth has advantage on saving throws against spells and other magical effects.

Magic Weapons. The Behemoth’s weapon attacks are magical.

Actions

Multiattack. The Behemoth makes three tentacle attacks.

Tentacle. Melee Weapon Attack: +15 to hit, reach 20 ft., one target.
Hit: 24 (4d6 + 8) bludgeoning damage. If the target is a creature, it is grappled (escape DC 19). Until the grapple ends, the target is restrained, and the Behemoth can’t use that tentacle on another target.

Eye of the Void (Recharge 5–6). The Behemoth emits a beam of maddening energy in a 90-foot line that is 5 feet wide. Each creature in the line must make a DC 20 Intelligence saving throw, taking 55 (10d10) psychic damage on a failed save, or half as much damage on a successful one. On a failed save, the creature is also blinded and stunned until the end of its next turn.

Bonus Actions

The Voidspawn Behemoth can use one of the following bonus actions on its turn:

• Abyssal Grasp (Recharge 4–6)
  The Behemoth targets a creature grappled by one of its tentacles. That creature must make a DC 19 Constitution saving throw or take 5d10 necrotic damage as its life force is drained, and its maximum HP is reduced by the same amount until it finishes a long rest.

• Call of the Void
  The Behemoth emits a low, subsonic pulse. One creature of its choice within 60 feet that can hear it must succeed on a DC 17 Wisdom saving throw or use its reaction to move up to its speed directly toward the Behemoth, avoiding obvious hazards. This movement does not provoke opportunity attacks.

• Voidphase Shift (Recharge 5–6)
  The Behemoth briefly phases into the Far Realm. Until the start of its next turn, it gains resistance to all damage, and it can move through objects and creatures as if they were difficult terrain.

Reactions

The Behemoth can use one of the following reactions when appropriate:

• Warping Counterstrike (When hit by a melee attack)
  The Behemoth lashes out with a writhing tentacle. The attacker must make a DC 18 Dexterity saving throw or take 4d6 psychic damage and be knocked prone as their perception of space twists violently.

• Reality Fracture (When reduced below half HP for the first time)
  The air around the Behemoth cracks like glass. All creatures within 20 feet must make a DC 19 Constitution saving throw or be blinded and deafened for 1 minute. They may repeat the saving throw at the end of each of their turns.

• Tentacle Reflex (When a creature enters its reach)
  The Behemoth makes one tentacle attack against a creature that enters its melee reach (20 ft) for the first time on their turn.

Legendary Actions

The Behemoth 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. It regains spent legendary actions at the start of its turn.

• Tentacle Slam. The Behemoth makes a tentacle attack.

• Warp Reality (Costs 2 Actions). The terrain in a 20-foot radius centered on a point the Behemoth can see within 120 feet becomes difficult terrain and filled with shifting, nightmarish illusions for 1 minute. Any creature that starts its turn in the area must make a DC 18 Wisdom saving throw or be frightened until the start of its next turn.

• Void Gaze (Costs 3 Actions). The Behemoth targets one creature it can see within 60 feet. The target must succeed on a DC 20 Charisma saving throw or be banished to a personal nightmare demiplane for 1 minute. While banished in this way, the target is incapacitated. The target can repeat the save at the end of each of its turns, ending the effect on a success.

Mythic Action Name. Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.