Body Mound

Necrotic Absorption. Whenever the Body mound is subjected to necrotic damage, it takes no damage and regains a number of hit points equal to the necrotic damage dealt.

Body Disposal. As a bonus action on each of its turns the Body mound can drop a body out of it. This body uses the zombie stat block and takes its turn on the Undead shambling mounds turn. As part of this bonus action the Body mound can control each of its zombies already released. 

Multiattack. The Body Mound makes two slam attacks. If both attacks hit a Medium or smaller target, the target is grappled (escape DC 14), and the shambling mound uses its Engulf on it.

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

Engulf. The Body mound engulfs a Medium or smaller creature grappled by it. The engulfed target is blinded, restrained, and unable to breathe, and it must succeed on a DC 14 Constitution saving throw at the start of each of the mound's turns or take 13 (2d8 + 4) bludgeoning damage. If the mound moves, the engulfed target moves with it. The mound can have only one creature engulfed at a time.

Grasping Hands.  As a reaction taken when a creature within 60ft of the Body mound or any of its zombies attempts to take its movement, the Shambling mound can make hands sprout up out of the earth grasping at the feet of all who are in a 10 ft radius centered on the targeted creature. The targeted creature must succeed on a DC 14 Strength Saving throw or be grappled. Regarldless if the creature succeeds or fails, the area is treated as rough terrain until the beginning of the Undead Shambling Mounds next turn.