Multiattack. The annelidast makes three Slam attacks.

Slam. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 21 (2d12 + 8) bludgeoning damage, and if the target is a creature, it must succeed on a DC 17 Strength saving throw or be pushed up to 15 feet away from the annelidast. A creature restrained by the annelidast automatically succeeds on this saving throw.

Crush (Recharge 5-6). The annelidast launches most of its massive bulk into the air and crashes down on the ground in a 20-foot line that is 10 feet wide. It then retracts itself into a space along that line and can occupy the space of one or more Large or smaller creatures. Each creature in the line must make a DC 17 Dexterity saving throw. On a failure, a creature takes 45 (7d12) bludgeoning damage, is knocked prone, and is restrained while it shares a space with the annelidast, as it is pinned beneath the annelidast's body. On a success, a creature takes half the damage, isn't knocked prone, and is pushed out of the annelidast's space into an unoccupied space of the creature's choice within 5 feet of the annelidast. A creature, including the restrained creature, can take its action to free the restrained creature by succeeding on a DC 17 Strength check. If the annelidast burrows along the surface of the earth at least 20 feet before using this action, creatures in the line have disadvantage on the saving throw.