Multiattack

The crystalline monolith makes two slam attacks or two mind spear attacks. If both slam attacks hit a Large or smaller target, the target must succeed on a DC 14 Constitution saving throw or begin to turn to crystal and be restrained. The restrained creature must repeat the saving throw at the end of its next turn, becoming petrified on a failure or ending the effect on a success.

Slam

Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 11 (2d8 + 2) bludgeoning damage.

Mind Spear

Ranged Spell Attack: +7 to hit, range 30 ft., one target. Hit: 14 (4d6) psychic damage.

Psychic Burst (Recharge 5-6)

The crystalline monolith emits a burst of psychic energy in a 30-foot cone. Each creature in that area must succeed on a DC 15 Intelligence saving throw or take 28 (8d6) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.