Multiattack

Two Trample attacks.

Trample

Melee Weapon Attack: +8 to hit, 5 ft., one target, 21 (3d10+5) bludgeoning damage.

Ballista Shot

Chooses up to two points it can see within 120' of it. The thunderer can't choose a point within 10 ft. of it. Each creature within 5 ft. of a point must make a DC 15 Con save taking 14 (4d6) necrotic on a failed save and half damage if made. If a creature is within 5 ft. of both points it has disadvantage on the save but it takes damage from only one effect not both.

Concentrated Shot (Recharge 5-6)

Picks a point it can see within 120' of it. Each creature within 20' of that point must make a DC 15 Con save. On a failure a creature takes 35 (10d6) necrotic and suffers one level of exhaustion. On a success a creature takes half the damage and doesn't suffer a level of exhaustion.