Multiattack

The shambling mound takes two slam attacks. If both attacks hit one Medium or smaller creature the target is grappled (escape DC 15) and the shambling mound uses Engulf against it.

Slam

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage.

Engulf

The shambling mound absorbs a Medium or smaller grappled creature into its body. The engulfed creature is blinded restrained can't breathe and moves with the shambling mound. At the start of each of the shambling mounds turns the target takes 11 (2d6 + 4) bludgeoning damage.