Death Burst. The shambling mound explodes when it drops to 0 hit points. Each creature within 20 feet of it must succeed on a DC 15 Constitution saving throw or take 28 (8d6) poison damage and become infected with a disease on a failed save. Creatures immune to the poisoned condition are immune to this disease. Spores invade an infected creature's system, killing the creature in a number of hours equal to 1d12 + the creature's Constitution score, unless the disease is removed. In half that time, the creature becomes poisoned for the rest of the duration. After the creature dies, it sprouts 2d4 Tiny gas spores that grow to full size in 7 days.

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.

Multiattack. The shambling mound makes two slam attacks. If both attacks hit a Medium or smaller target, the target is grappled (escape DC 17), and the shambling mound uses its Engulf on it.

Slam. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) bludgeoning damage plus 4 (1d8) poison 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 17 Constitution saving throw at the start of each of the mound's turns or take 14 (2d8 + 5) bludgeoning damage plus 4 (1d8) poison damage. If the mound moves, the engulfed target moves with it. The mound can have only one creature engulfed at a time.