Multiattack

The sand silhouette makes two slam attacks.

Slam

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 14 (3d6 + 4) bludgeoning damage. If both attacks hit a Medium or smaller target, the target is grappled (escape DC 14), and the sand silhouette engulfs it.

Engulf

The sand silhouette engulfs a Medium or smaller creature grappled by it. The engulfed target is blinded and restrained, but no longer grappled. It must make a successful DC 15 Constitution saving throw at the start of each of the sand silhouette's turns or take 14 (3d6 + 4) bludgeoning damage. If the sand silhouette moves, the engulfed target moves with it. The sand silhouette can only engulf one creature at a time.

Haunted Haboob (Recharge 4-6)

The sand silhouette turns into a 60-foot radius roiling cloud of dust and sand filled with frightening shapes. A creature that starts its turn inside the cloud must choose whether to close its eyes and be blinded until the start of its next turn, or keep its eyes open and make a DC 15 Wisdom saving throw. If the saving throw fails, the creature is frightened for 1 minute. A frightened creature repeats the Wisdom saving throw at the end of each of its turns, ending the effect on itself on a success.