Psionic Mastery. The Voidreaper Colossus can cast psionic spells as a 9th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). It requires no components to cast its spells. The colossus knows the following spells:

1. At will: telekinesis, detect thoughts, minor illusion
2. 3/day each: dominate person, hallucinatory terrain, teleport
3. 1/day: mass suggestion, power word stun

Gravity Manipulation. The colossus can use its bonus action to create a 20-foot-radius gravity well centered on itself. The area becomes difficult terrain, and creatures within it must succeed on a DC 16 Strength saving throw or be restrained until the start of their next turn.

Abyssal Rift. As an action, the colossus can open a rift to the void within 60 feet of itself. Tendrils of darkness lash out from the rift, targeting up to three creatures the colossus can see within 30 feet of the rift. The targeted creatures must make a DC 16 Wisdom saving throw or be paralyzed for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on a success.

Multiattack. The colossus makes two slam attacks.

Slam. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 19 (3d8 + 5) bludgeoning damage plus 10 (3d6) psychic damage.

Gravity Pulse (Recharge 5-6). The colossus releases a surge of gravitational energy in a 30-foot cone. Each creature in the cone must succeed on a DC 16 Dexterity saving throw, taking 27 (6d8) force damage on a failed save, or half as much on a successful one. On a failed save, a creature is also pushed 10 feet away from the colossus and knocked prone.

Ethereal Phasing. As a reaction when it takes damage, the colossus can shift partially into the ethereal plane until the end of its next turn, becoming resistant to all damage except radiant. It can move through other creatures and objects as if they were difficult terrain.

Aura of Desolation. At the start of each creature's turn within 30 feet of the colossus, they must make a DC 16 Wisdom saving throw or have disadvantage on their next saving throw before the start of their next turn.