Shambling Mound

Large plant, unaligned

Armor Class 15 (natural armor)
Hit Points 136 (16d10 + 48)
Speed 20 ft., swim 20 ft.

Skills Stealth +2
Damage Resistances cold, fire
Damage Immunities lightning
Condition Immunities blinded, deafened, exhaustion
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 10
Languages --
Challenge 5 (1,800 XP)

Lightning Absorption. Whenever the shambling mound is subjected to lightning damage, it takes no damage and regains a number of hit points equal to the lightning damage dealt.

Actions

Multiattack. The shambling 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 shambling 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.