Blood and Muck - RSP Encounter

As PCs journey along a causeway through a marsh comprising stretches of deep bog interspersed with areas of shallow bog, they come to the attention of a shambling mound preying on travelers. The shambling mound is not alone for it has recently slain a pair of lizardfolk and swarms of leaches now feed upon their decomposing remains.

Area Features

Foreboding Mists: Fog blankets the swamp. The fog obscures all sight beyond 40 feet, including darkvision. Creatures 10 feet away have concealment (20% miss chance).
Bogs - shallow: The shallow bog is considered difficult terrain and also increases the DC of stealth checks by 2. Bogs - deep A square that is part of a deep bog has roughly 4 feet of standing water. It costs Medium or larger creatures half of their movement to enter such squares or they can swim (DC 10 Athletics/Swim check). Small or smaller creatures must swim to move through a deep bog. The water in a deep bog provides cover for Medium or larger creatures. Smaller creatures get half cover. Medium or larger creatures can crouch as a move action to gain improved cover. Deep bogs increase the DC of Stealth checks by 2.
Massive Mangroves The huge trees (DC 15 Acrobatics to climb) fill an entire square. Lizardfolk Corpses The corpses have been partially eaten and the cadavers are now horribly decomposed. A few leaches yet linger on the remains but not enough to injure the PCs. Sunken Treasure A PC searching in the vicinity of the corpses must make a DC 25 perception check to discover the lizardfolk's treasure, which has sunk into the mire.

You trod down the 10-ft high, 5 foot wide steeply sloped causeway. The causeway is built from a pile of stone, each roughly a foot in diameter. Climbing or descending the causeway does not require a climb check but is considered difficult terrain. The path cuts through a low-lying area of boggy marsh. Tall trees occasionally rear from the rank, fetid smell of swamp water assaults your senses. Make a Perception check (DC 15 Perception check) Twenty feet from the causeway, the decomposing bodies of two lizardfolk float amongst the filth.

When the PCs reach the area, the shambling mound is lurking at the base of a large tree (Stealth +16) while the leach swarm (Stealth +24) feeds on the decomposing lizardfolk. The two large leaches hide nearby in an area of deep bog similarly waiting for prey to enter the water.

TACTICS

The shambling mound attacks as soon as any creature enters the bog. It seeks to grab a tasty snack as quickly as possible and to drag it into a deep pool there to feed upon it. If the PCs flee the mire, it attacks the nearest giant leach. As soon as it detects movement in the water the leach swarm leaves the drained lizardfolk and attacks – seeking fresh blood. They ignore the shambling mound, and it ignores them.
The giant leaches arrive two rounds after combat begins and attack the nearest creatures in the water seeking to drink their blood. They stay away from the shambling mound (which views them as food). The leaches attack until slain, but the shambling mound flees if reduced to one-quarter hit points.

Treasure

Pouch of Gems: Four transparent dark green stones (bloodstones worth 50 gp each) and an orange translucent stone (a garnet worth 200 gp) lie in a waterlogged, muddy pouch. A DC 20 Appraise check values and identifies each type of gem.
Emerald Statuette: This exquisitely carved finger-sized statue is of green transparent stone (emerald). It depicts a lizardfolk female heavy with child. A DC 15 Knowledge (religion) reveals it depicts the lizardfolk’s fertility goddess and the statuette has great significance to a local tribe Ziuanthi Lizardfolk; its return will earn the PCs the tribe’s grateful thanks (and possibly even tribal membership). A DC 20 Appraise check values it at 2,000 GP, however.

SHAMBLING MOUND CR: 5 (1,800XP)

Large plant, unaligned

Armor Class: 15 (Natural Armour)

Hit Points: 136 (16D10+48)

Speed: 20 ft , swim: 20 ft

STR

18 +4

DEX

8 -1

CON

16 +3

INT

5 -3

WIS

10 +0

CHA

5 -3

Skills: Stealth +2

Damage Resistances: Cold & Fire

Damage Immunities: Lightning

Condition Immunities: Blinded,Deafened & Exhaustion

Senses: Blindsight 60ft (Blind beyond this radius) & Passive Perception 10

Challenge Rating: 5 (1,800XP)

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 5FT, 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.

Leech CR: 1/8

Tiny beast, any

Armor Class:

Hit Points:

Speed: 5 ft , swim: 20 ft

STR

3 -4

DEX

10 +0

CON

8 -1

INT

3 -4

WIS

9 -1

CHA

3 -4

Skills: Stealth +2

Condition Immunities: Blinded

Senses: Blindsight 20 ft. (Blind beyond this radius) Passive perception 9

Challenge Rating: 1/8

Actions

Bite: Melee Weapon Attach: +2 to hit. Reach 5 ft., 1 creature. Hit: 1d4 piercing damage and the leech attaches to the target. While attached, the leech doesn't attack. Instead, at the start of each of the leech's turns, the target looses 1d4 hit points due to blood loss.
The leech can detach itself by spending 5 feet of its movement. It does so after it drains 8 hit points of blood from the target or the target dies. A creature, including the target, can use its action to detach the leech.

Leeches can be found swimming through murky waters and crawling through the mud. In some places people use them for medicinal purposes. Their gigantic variation is often encountered in swamps and sometimes on other planes of existence where the planar magic changes their physical size.

Giant Leech CR: 2

Large beast, any

Armor Class: 14

Hit Points: 60

Speed: 15 ft , swim: 40 ft

STR

13 +1

DEX

8 -1

CON

14 +2

INT

3 -4

WIS

9 -1

CHA

3 -4

Skills: Amphibious. The leech can breathe air and water.

Condition Immunities: Blinded

Senses: Blindsight 30 ft. (Blind beyond this radius) Passive Perception 9

Challenge Rating: 2

Actions

Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 3d6 piercing damage. When the target is Medium or smaller they have to make a strength saving throw (DC13). On a failed save they are swallowed by the leech.
Swallow. A swallowed target is blinded and restrained. It has total cover against attacks and other effects outside the leech. The creature takes 2d6 piercing and 2d6 poison damage at the start of each of the leech's turns. The leech can have only one target swallowed at a time. if the leech dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 6 feet of movement, exiting prone.

Unlike its smaller counterpart, a giant leech tends to swallow a creature whole to drain it of its blood. For this purpose, the entire inside of the leech is lined with rows of sharp teeth. 

Suggested Environments

Leeches can be found swimming through murky waters and crawling through the mud. In some places people use them for medicinal purposes. Their gigantic variation is often encountered in swamps and sometimes on other planes of existence where the planar magic changes their physical size.