Sandstorm. A sandstorm surrounds the horse in a 20-foot radius. The area is heavily obscured, and creatures other than the horse that start their turn within the aura must succeed on a DC 19 Constitution saving throw or take 21 (6d6) slashing damage from the biting sands.

Sand Conversion. The horse turns the terrain it passes over into difficult terrain as dirt and stone become loose sand. Each square of dirt or stone that the Harbinger moves over becomes sand for 1 month.

Trampling Charge. If the horse moves at least 20 feet straight toward a creature and then hits it with a hooves attack on the same turn, that target must succeed on a DC 14 Strength saving throw or be knocked prone. If the target is prone, the horse can make another attack with its hooves against it as a bonus action.

Hooves. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 21 (4d6 + 6) bludgeoning damage.