Amphibious. The Voidfish can breathe air and water.

Destroy Memories. Any written information that the Voidfish swallows and digests is forgotten. No creature can remember or learn this information, only hearing static noise whenever the information is referenced. A creature that drinks from the Voidfish's ichor can learn the information or regains its memories of it if it had any.

Innate Spellcasting. The Voidfish's spellcasting ability is Wisdom (spell save DC 20). The Voidfish can innately cast the following spells, requiring no material components:

At will: calm emotions, detect thoughts, levitate,
modify memory
3/day each: telekinesis, sending
1/day each: modify memory (9th level), feeblemind

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

Probing Telepathy. If a creature communicates telepathically with the Voidfish, the Voidfish learns the creature's greatest desires if the Voidfish can see the creature.

Sanctuary. Any creature who targets the Voidfish with an attack or a harmful spell must first make a DC 20 Wisdom saving throw. On a failed save, the creature must choose a new target or lose the attack or spell. This feature doesn't protect the voidfish from area effects, such as the explosion of a fireball. If a creature succeeds on its saving throw, it becomes immune to this effect for 1 minute.

Multiattack. The Voidfish makes four tentacle attacks.

Tentacle. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 18 (4d6 + 4) bludgeoning damage
plus 7 (2d6) psychic damage.

Mind Blast (Recharge 5-6). The Voidfish magically emits psychic energy in a 30-foot-radius centered on it. Each creature in that area that the Voidfish chooses must succeed on a DC 20 Intelligence saving throw or take 55 (10d10) psychic damage, or half as much damage on a successful save. A creature that fails its saving throw automatically fails its next saving throw against the Voidfish's Sanctuary feature.

 The Voidfish can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn.The Voidfish regains spent legendary actions at the start of its turn.

Detect. The Voidfish makes a Wisdom (Perception) check.

Tentacle. The Voidfish makes one tentacle attack.

Assail Memories (Costs 2 Actions). The Voidfish targets one creature it can see within 120 feet of it. The creature must make a DC intelligence saving throw. It takes 22 (4d10) psychic damage on a failed save, or half as much on a successful one. A creature that fails its saving throw automatically fails its next saving throw against the Voidfish's Sanctuary feature.