Mind Frenzy. The shark has advantage on melee attack rolls against any creature that has a Wisdom score of 8 or less.

Water Breathing. The shark can breathe only underwater.

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

Innate Spellcasting (Psionics). The shark's innate spellcasting ability is Intelligence (spell save DC 15). It can innately cast the following spells, requiring no components:

At will: detect thoughts, levitate, bane

1/day each: modify memory, confusion

Underworld Sight. The shark can see through magical and non-magical darkness with it's darkvision.

Multiattack. The shark makes two attacks, one with it's tentacle and one with it's bite.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) piercing damage. The target must make a DC 18 intelligence saving throw, taking 14 (4d6) psychic damage on a failed save, or half as much on a successful one.

Tentacle. Melee Weapon Attack: +8 to hit, reach 20 ft., one target. Hit: 14 (4d6) psychic damage. The target must then make a DC 18 charisma saving throw. On a failed save, the creature's wisdom score decreases by 2 to a minimum if 3 and it must roll and subtract a d6 for each it's ability checks, attack rolls, and saving throws. These effects each last until the creature finishes a long rest, and are ended early by a greater restoration spell, a remove curse spell, or similar magic.

If the creature fails by 5 or more or the reduction to the wisdom score reduces it to 3, it forgets everything that happened within the last day. Each time this happens, the creature forgets one more day.

Levitate (3/day). Before the shark takes damage, it can use it's reaction to levitate 15 feet into the air. If this would cause it to not take damage, it avoids the damage and the creature that would have dealt the damage takes 14 (4d6) psychic damage.

The shark harmlessly floats back to the ground at the start of it's next turn.