Multiattack

Two Chain Lash attacks.

Chain Lash

Melee Weapon Attack: +8 to hit, 15 ft., one target, 18 (4d6+4) slashing damage and the target is grappled (escape DC 15). The reaver has four chains each of which can grapple only one target.

Bladed Sweep (Recharge 5-6)

Swings its chains in a wide arc. Each creature within 15 ft. of the reaver must make a DC 15 Dex save. On a failure a creature takes 21 (6d6) slashing damage and is knocked prone. On a success a creature takes half the damage and isn't knocked prone. A creature that fails the save by 5 or more is pushed up to 15 ft. away from the reaver and knocked prone.