By Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging
encounters against a Darkmantle
Note: This has been prepared utilizing only the 5E Core Rules. The Darkmantle can be found in the Monster Manual page 46. Additional lore information has been drawn from previous editions of the Dungeons and Dragons game to include Pathfinder.
Primarily found in the Underdark, the Darkmantle occupies an ecological niche like that of a bat. Usually they subsist on vermin and other small creatures. While the Darkmantle has rudimentary eyes that can detect light, they like bats are primarily echolocators relying on sound reflection as their primary sensory capability.
Darkmantles are ambush predators and are not aggressive. As with all ambush predators, they instinctually attack when they either find isolated prey, or when they can isolate a prey animal. Since their primary purpose is to consume what they hunt, their instinct, coupled to their minimal intelligence has given them cunning enough to understand that merely killing a meal is not enough, they need to be able to consume it as well.
Darkmantles are usually found in small groups call ‘Scourges’. These groupings are usually migratory, as they will rapidly deplete an area of available prey, forcing relocation. Intelligent denizens of the Underdark have been known to plant or to allow a Darkmantle Scourge to flourish in some of the smaller approaches to their larger cavern lairs. This provides them with a passive guard force that both guards a disused entry and controls the vermin that might otherwise propagate.
While some horror stories of a Darkmantle scourge that occupied a cavern many acres wide have been told, the actual existence of such a grouping as a natural occurrence is highly doubtful. They would simply run out of prey and starve.
Darkmantles nest in high clefts that overlook their hunting grounds. Ideally, these are located above a natural hazard such as a cliff path that can be used to assist the kill.
Darkmantles are highly adaptable, their rapid lifespan when coupled to the Underdark environment has provided a huge variety of these creatures, some with the ability to swim, some with tougher hides, some with greater speed, even some with fire resistance or cold resistance. Despite this adaptability, it is assumed that the Darkmantle are a created form of life, the object of some experiment that was abandoned or went wrong in time outside of living memory.
Darkmantle skins are known to be used in the fabrication of the Magical item “Cloak of the Bat”.
Step 1) Let’s Review what we know about the Darkmantle.
While small, a mere forty pounds and at largest a six-foot wingspan, these creatures are extremely strong (16). They are above average in Dexterity and Constitution. Based on their intelligence level, Charisma and Wisdom. It can be concluded that they are instinctual ambush hunters that live in communities and are adaptable to their environment. They do not PLAN per se, but merely recognize preferred hunting grounds.
Darkmantle are hard to spot due to their natural stealth ability (+3) and their FALSE APPEARANCE ability, which makes them indistinguishable from natural cave formations such as Stalactites and Stalagmites if they remain motionless.
Darkmantle have vestigial eyes that allow them to differentiate light and darkness but perceive instead by echolocation. This gives them BLINDSIGHT at a range of sixty feet. Note that mere loud noise or cacophony will not accomplish it, but it is possible to render them BLIND by creating a condition that DEAFENS them. Their passive perception score is 10, reminder, it is not dependent on vision or light.
Darkmantle have a natural ability to create a magical darkness (ten-foot radius) centered on themselves. Naturalists compare this ability to the ability of octopi to create an ink cloud, though the fact that the effect travels with the creature is clear evidence of magical involvement.
Darkmantle can fly (thirty feet per round normally), moving through the air much the way an octopus swims, using great concentric flaps of its wing surface. The sound of this flapping is distinctive and is recognizable to those who are familiar with the underdark environment.
Darkmantle are ungainly when grounded, moving at a mere ten feet per round.
Step 2) Determine the probable Strategy.
As with all Ambush predators, the Darkmantle will wait in stealth and utilize its FALSE APPEARANCE ability to remain undetected until it detects an opportunity in which its attack is likely to succeed (Wisdom 10).
This usually means that the Darkmantle has or can isolate its prey or it means that it has a terrain feature that it can use to assist in the kill.
An oft overlooked feature of these creatures is that while they normally attack from above, they can also attack from the ground or pounce from the side.
Step 3) Determine Tactics
Waiting for the proper moment, the Darkmantle will attack only medium or small (preferred) creatures that are isolated or solitary. As a rule, based on echolocation, the less massive the target, the more likely it is to be the target. Additionally, as the Darkmantle intends to attack the head, it can and will avoid those targets wearing metal helms or other protections over the head.
Attacking from Hiding (FALSE APPEARANCE), and thus with ADVANTAGE, the Darkmantle will attempt to engulf the targets head. If successful, the Target will be affected by the BLINDED condition, and will be unable to breath (SUFFOCATION).
SUFFOCATION (PHB page 183) forces a creature to hold its breath. After a time equal to 1 + the Constitution Modifier or a Minimum of 30 seconds (whichever is longer) the creature drops to ZERO hit points and is dying. It cannot be stabilized or regain HP until it can breathe.
While attached to the target, the Darkmantle is unable to move of its own volition and will instead be able to move as the target moves. Therefore, the Darkmantle prefers to attack cliffside; a blinded struggling target can easily fall. The Darkmantle, using both its ability to fly and echolocation will avoid the impact with the ground by expending a mere 5 feet of its movement.
While the Darkmantle is capable to squeezing and attacking the victim further, it will usually choose to DODGE and HOLD onto the target instead, relying on the suffocation incapacitate the victim feasting once their target is dead. If the Darkmantle chooses to ATTACK, then all its attacks are made at ADVANTAGE.
A Darkmantle can be successfully dislodged from the head of a victim by a Successful DC 13 Strength Check taken as an action).
Step 4) DM Tips and Observations
The Adaptability provides the DM with the ability to vary this creature greatly, using it as a template to create larger versions, versions resistant to environmental factors such as Heat, Cold, Poisonous Gasses, or Acid. It is recommended that you increase the CR and XP reward for such modified versions.
The ENGULF ability is better handled as a RESISTED STRENGTH CONTEST vs a Standard DC 13 Strength Check. If you do so, the Darkmantle should be given ADVANTAGE on the Contest Checks.
The best use of this creature is as a passive means of keeping the party together. Rogues, Monks and other lightly armored personnel are likely to wander and explore away from the group creating the added and difficult complication of effectively running two games at the same time. If the characteristic ‘WHOSH’ of Darkmantle flight is heard in the distance, these poorly armored and often physically weak characters may realize that wandering off alone, especially without backup available, is a dangerous undertaking.