Shambling Mound 5e: Engulf, Lightning Absorption and the Swamp Ambush

A shambling mound is a CR 5 Large plant with AC 15, 136 hit points (110 in 2024), resistance to cold and fire, and a trait that turns the party's lightning spells into healing: Lightning Absorption. It fights by grabbing a creature and swallowing it into its rotting mass. In 2014 it needs both slams to hit before it can do that, and the swallowed creature is crushed and can't breathe. The 2024 version has three 10-foot tendrils that drag victims in and an Engulf that works on a single failed Strength save, and the creature inside takes lightning damage every turn.

Table of Contents

• •Shambling Mound Stat Block (2014)
• •Shambling Mound in the 2024 Rules
• •Lightning Absorption, Explained
• •How Engulf Works in Each Edition
• •How Shambling Mounds Fight
• •Running a Shambling Mound Encounter
• •How Players Beat a Shambling Mound
• •Shambling Mound Encounter Ideas
• •Frequently Asked Questions

Shambling Mound Stat Block (2014)

The SRD 5.1 shambling mound, the same as the 2014 Monster Manual.

Two things define it. First, the defensive profile: AC 15, 136 hit points, resistance to the two most common blasting elements and immunity to a third. A level 5 wizard's Fireball does half damage, and a Lightning Bolt heals it. Second, it's slow: 20 feet on land and in water. It is an ambusher that waits in a bog, not a hunter that chases.

Its only senses are blindsight out to 60 feet. Beyond that range it is blind.

Shambling Mound in the 2024 Rules

SRD 5.2.1 keeps the CR, AC, resistances and lightning immunity but rebuilds its attacks.

The 2024 mound has fewer hit points but is much more active. It moves 50% faster, reaches 10 feet, attacks three times, and engulfs on a save rather than on two hits. It also loses its immunity to the Blinded condition, so an effect like Blindness/Deafness can now land on it.

Lightning Absorption, Explained

2014: whenever the mound is subjected to lightning damage, it takes no damage and regains hit points equal to the lightning damage dealt.

2024: whenever it is subjected to lightning damage, it regains hit points equal to the lightning damage dealt. It still takes none, because it has immunity to lightning.

In both editions, the important word is "dealt". A Lightning Bolt that would deal 28 heals the mound for 28. If the mound makes its save and would take half, it heals 14. Call Lightning every round is a heal every round.

This has three table consequences:

• •Players who don't know will heal it. A sorcerer who opens with Lightning Bolt into the swamp has just given the mound 28 hit points. Let them see the vines knit back together. They'll remember.
• •Enemies can heal it on purpose. A cultist or druid NPC with lightning spells can blast the party through the mound, catching the party and healing their plant ally in the same action.
• •The 2024 engulfed victim isn't the mound. The 3d6 lightning damage a swallowed creature takes is dealt to the victim, so it doesn't heal the mound.

How Engulf Works in Each Edition

2014 Engulf

1. •The mound makes two Slam attacks. At +7 against AC 16, each hits on a 9 or higher, 60%. Both hit 36% of the time.
2. •If both hit the same Medium or smaller creature, that creature is grappled (escape DC 14) and the mound uses Engulf on it immediately, as part of the same Multiattack.
3. •The engulfed creature is Blinded and Restrained and can't breathe. It moves with the mound.
4. •At the start of each of the mound's turns, it makes a DC 14 Constitution saving throw or takes 13 (2d8 + 4) bludgeoning damage. A character with +2 Constitution passes on 12 or higher, 45%.
5. •The mound can hold only one engulfed creature.

Getting out. The stat block gives the grapple an escape DC of 14, but the Engulf text never says when being engulfed ends. It only says Engulf works on a creature the mound is grappling.

DM ruling, not rules text: we recommend treating a successful grapple escape as also ending the engulf (the creature climbs out of the mound into an adjacent space). Nothing in SRD 5.1 says this. Decide it before the fight and tell the player when their character is swallowed.

Escaping the grapple uses the 2014 rules: an action and a Strength (Athletics) or Dexterity (Acrobatics) check against DC 14. Restrained doesn't impose disadvantage on that check, so a character with +5 Athletics escapes on a 9 or higher.

About breathing. Under the SRD 5.1 suffocation rules, a creature can hold its breath for 1 + its Constitution modifier minutes (minimum 30 seconds). That's at least five rounds, so suffocation rarely matters before the fight ends. It matters if the mound swallows someone and wanders off into the swamp: once the breath runs out, the creature survives a number of rounds equal to its Constitution modifier (minimum 1), then drops to 0 hit points.

2024 Engulf

1. •The mound's Multiattack is three Charged Tendril attacks, and it can replace one with Engulf.
2. •Each tendril that hits a Medium or smaller creature pulls it 5 feet toward the mound. A creature 10 feet away is now 5 feet away, which is inside Engulf's range.
3. •Engulf targets one Medium or smaller creature within 5 feet: DC 15 Strength save. A character with a +3 Strength save passes on 12 or higher, 45%. One with a −1 Strength save passes on 16 or higher, 25%.
4. •On a failure the creature is pulled into the mound's space and Grappled (escape DC 14). Until the grapple ends it is also Blinded and Restrained, and it takes 10 (3d6) lightning damage at the start of each of its own turns.
5. •The mound carries the grappled creature at no extra movement cost. It can only have one creature engulfed at a time.

Getting out. In 2024 this is clean: escaping the grapple ends the Blinded and Restrained conditions too. The victim uses its action for a Strength (Athletics) or Dexterity (Acrobatics) check against DC 14. The lightning hits at the start of the turn, so the victim always takes at least one 3d6 before its first escape attempt.

How Shambling Mounds Fight

Damage per round, against AC 16.

For the 2014 mound, add the Engulf crush on top: an engulfed creature that fails the DC 14 Constitution save takes another 13 at the start of each of the mound's turns.

Ambush from the water. Stealth +2 (or +3), a swim speed and a body made of swamp muck make the mound a natural ambusher. Put it in a reed bed, a drainage cistern or a flooded crypt, and roll its Stealth against the party's passive Perception.

2024 turn order: pull, swallow, hit. The best 2024 turn starts with a tendril against someone at 10 feet. If it hits, the target is now 5 feet away. The second attack is Engulf. The third attack goes against the swallowed creature (Restrained, so Advantage) or someone else in reach.

Swallow the caster, then leave. With a creature inside, the mound should retreat into deep water or thick undergrowth, carrying its victim. The party has to chase it through difficult terrain while their friend takes damage every round. The 2014 mound moves only 20 feet, so this works best when it starts close to water.

Pick Medium or smaller targets. Both versions can only engulf Medium or smaller creatures. A Large mount, a druid in a Large wild shape or an enlarged fighter is immune to the swallow.

Running a Shambling Mound Encounter

A shambling mound is worth 1,800 XP. Using the 2024 SRD 5.2.1 budget for four characters:

The 2014 Dungeon Master's Guide guidelines put one mound against four level 5 characters at Easy (1,800 XP is under the 2,000 Medium threshold) and against four level 4 characters at Hard. You can try other party sizes in the encounter difficulty calculator.

Party composition matters more than XP here. A party whose damage comes from Fireball and Lightning Bolt will find a mound much tougher than the numbers say. A party of sword users will find it straightforward.

How Players Beat a Shambling Mound

Know its damage profile.

Weapons work fine. It has no resistance to physical damage at all.

Blight is the specialist spell. Blight (4th level) is brutal against plants. In 2014, a plant creature makes the save with disadvantage and takes maximum damage: 64 necrotic. In 2024, a plant creature automatically fails the save and takes 8d8, an average of 36.

Stay out of reach. In 2014 its reach is 5 feet and it moves 20. In 2024 its reach is 10 feet and it moves 30. Either way, characters at range can keep away from it, especially in a swamp where difficult terrain slows it too.

Attack from beyond 60 feet. Blindsight 60 feet is its only sense. A character more than 60 feet away is someone it can't see, and attacks against a creature that can't see you have Advantage.

Free the swallowed character fast. In 2024, every round inside costs 3d6 lightning, and in 2014 every failed save costs 13. The victim should spend its action escaping (DC 14). Everyone else should focus damage on the mound. Be careful with area spells: in 2024 the swallowed character is pulled into the mound's space, and in 2014 it moves wherever the mound goes, so a blast centered on the mound usually catches it too. Avoid splitting the party's damage between the mound and anything else until the victim is out.

Don't stand in a cluster near water. A mound that rises out of a pond in the middle of the party gets attack options against everyone. Keep the party's spellcasters on dry, open ground.

Shambling Mound Encounter Ideas

The lightning-rod tower. A ruined wizard's tower in a marsh has an iron spire that draws lightning in every storm. Over the years three mounds have grown fat on it and hold the ground floor. During a storm, any mound that reaches the spire's base is healed by every strike. The party can break the spire (iron, AC 19 on the SRD's Object Armor Class table) or fight in the rain on the mounds' terms.

The ferryman's warning. A ferryman poles travelers across a black-water marsh for a silver piece, and he never stops at the small island halfway across. The island is a mound that has been growing for decades. Anyone who insists on landing to camp gets an ambush at night, out of the water, rolling its Stealth against the passive Perception of whoever is on watch.

The druid's compost. An NPC druid is "protecting" a shambling mound she believes is a sacred spirit of the fen. She heals it with Call Lightning when it fights. The party can kill both, persuade her she's wrong, or help her move the mound somewhere it can't eat villagers' goats.

Frequently Asked Questions

What CR is a shambling mound in 5e?

A shambling mound is CR 5 (1,800 XP) in both editions. It has AC 15 and 136 hit points in 2014 or 110 in 2024.

Does lightning heal a shambling mound?

Yes. Its Lightning Absorption trait means lightning damage deals no damage to it and instead heals it for the amount that would have been dealt. This is true in both 2014 and 2024.

How do you escape a shambling mound's engulf?

Escape the grapple: use your action to make a Strength (Athletics) or Dexterity (Acrobatics) check against DC 14. In 2024, ending the grapple also ends the Blinded and Restrained conditions. The 2014 text doesn't say when being engulfed ends, so whether escaping the grapple also frees you is the DM's ruling.

Is a shambling mound resistant to fire?

Yes. It resists fire and cold damage and is immune to lightning in both editions. Slashing, piercing and bludgeoning weapons, thunder, acid, necrotic and radiant damage all work normally.

What's the difference between a shambling mound and a treant?

Both are plants, but they play very differently. A shambling mound (CR 5) is a swamp ambusher that swallows victims and heals from lightning. A treant (CR 9) is a Huge, intelligent forest guardian that hits structures for double damage and animates trees, and it is vulnerable to fire rather than resistant.

Stat blocks: System Reference Document 5.1 (2014) and 5.2.1 (2024), Wizards of the Coast, CC-BY-4.0. Tactics, encounter math and ideas are Loreify's own.