The Underdark is home to some of the most influential creatures of Dungeons & Dragons lore. The brain-eating mind flayers and all-powerful beholders claim this area as their home along with the drow and the duergar. With so many powerful beings, the Underdark is a perfect location for high-level D&D adventures.

As the Monster Manual says, "There is no greater dungeon than the Underdark." The subterranean world houses enough territory and creatures to fill an entire D&D campaign. The creatures that reside there are only one part of its alien nature and the very terrain itself can be hostile to adventuring parties. Any creature at home in the Underdark will be made even more powerful when used in conjunction with twisting tunnels, toxic fungi, or sudden rockslides. All these factors can help an Underdark creature present a threat beyond what its challenge rating might suggest.

Updated by Louis Kemner on September 5th, 2023: This list of the best Underdark monsters has been updated to match CBR' current publication standards, along with five more entries of the coolest and scariest Underdark creatures a party could meet in any D&D 5e campaign.

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20 Grimlock

CR: 1/4

A Grimlock from Dungeons & Dragons

Grimlocks are fine opponents for low-level parties who are only prepared to fight weak monsters early in a D&D 5e campaign. These humanoid monsters are what remain of the mind flayers' worshipers, who fled to the Underdark to avoid constant war with the rest of the world.

Grimlocks are completely blind but have sharp hearing and strong noses, so they can easily track a party of intruders in their realm. They're also immune to sight-based trickery or debuffs such as illusion spells, for example. They can also easily hide in rocky terrain, making them decent ambush hunters as well.

19 Grick

CR: 2

a grick is screeching in D&D

Gricks are tough, worm-like Underdark monsters that have deadly beaked mouths and four suckered tentacles on their heads for grasping prey. Even more so than grimlocks, gricks are excellent ambush hunters in the Underdark, blending in with the rocky terrain until they lunge at their prey or drop down from above.

Gricks often have lairs and might have a messy hoard of treasure and perhaps some magic items left over from their previous victims. Some adventurers will find and seal off a grick's lair, and wait for the gricks inside to starve to death. Then, the adventurers can help themselves to the grick's hoard, a tactic that cunning D&D parties might try for themselves.

18 Black Pudding

CR: 4

Black pudding devours unsuspecting orc

Black puddings are roughly similar to gelatinous cubes, but with an even more sinister edge as eerie Underdark creatures. Like gelatinous cubes, black puddings are mindless eaters that simply rove around at random, without any strategy in mind. Also, like gelatinous cubes, many black puddings retain the coins and other items of their victims, which provides great payoff for anyone who actually kills that pudding.

In the Underdark, black puddings usually just mind their own business, but clever creatures might use them as unwitting guard dogs against intruders, or simply use them for waste disposal. However, if the demon lord Juiblex is around, black puddings become a little smarter and act more purposefully.

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17 Wraith

CR: 5

a dark wraith in dungeons and dragons

Even when compared to most other Underdark monsters, wraiths are truly wicked and horrifying beings with no hope of redemption. Wraiths are all that remain of mortals who are condemned to the Lower Planes, retaining nothing of their previous identities. In this form, the person turned wraith wants just one thing -- to extinguish life.

Wraiths are misty, dark creatures that rove around, withering all plants and scaring off animals of all kinds. These Underdark creatures might also lead their fellow undead in battle. In gameplay, wraiths have a lot of resistances and few weaknesses, though they can't stand sunlight.

16 Warlock of the Great Old One

CR: 6

a warlock of the great old one

Warlocks of the Great Old One can appear in a variety of terrain types, but if a campaign takes place in the Underdark, then that's where the party will meet these wicked magic users. Warlocks of the Great Old One can be any race and any alignment, though for Underdark flavor, they will probably be either drow or duergar.

Warlocks of the Great Old One sometimes worship their deities alongside aberrations, while others seek to undermine their own patrons, which could lead to some intriguing plot twists in any D&D 5e Underdark campaign. Combat-wise, these warlocks are formidable with their daggers, which can be used either up close or as thrown weapons, dealing piercing and psychic damage with each hit.

15 Umber Hulk

CR: 5

dnd umber hulk an insectoid creature

The best monsters in D&D are more than just big bruisers. Not every creature can be a spellcaster, but it's fun when even the most straightforward-seeming creatures have some kind of hook that sets them apart. The umber hulk is a D&D staple, dating all the way back to the early days, and it packs a powerful backup ability in addition to its melee strength.

These giant insects are powerful combatants, but they really shine with their Confusing Gaze trait. Anyone who looks at an umber hulk is beguiled by its eyes and forced to take a random action. These creatures can tunnel through solid rock, so an Underdark-based D&D campaign could feature an umber hulk ambush at any time, forcing the players to stay on their toes.

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14 Cloaker

CR: 8

dnd cloaker flying manta ray creature

Blurring the line between creature and trap, a cloaker is a large subterranean predator that resembles a cloak when it stays motionless. Anyone who draws near, however, will find themselves immediately set upon by a monstrous creature that attempts to suffocate its prey by engulfing them.

Cloakers also emit a dreadful moan that can inflict fear in anyone who hears it. To make them even harder to pin down, cloakers can create illusory copies of themselves. A low- or mid-level D&D party trapped in the Underdark could easily be killed by just one or two cloakers.

13 Shadar-Kai

CR: 9 - 11

DnD Shadar Kai in a dark alley

The shadar-kai were once elves that worshiped The Raven Queen, but they now reside in the dark plane of the Shadowfell. Most of them still serve the Raven Queen, scouting the planes for souls who may be of interest to her. Since they are most at home in the deep darkness, shadar-kai make great Underdark foes.

Shadar-kai shadow dancers fight with their signature spiked chains and can use them to restrain their opponents or inflict immense amounts of necrotic damage. Gloom weavers and soul mongers are both powerful spellcasters, providing a great threat to anyone who opposes the will of the Raven Queen.

12 Oinoloth

CR: 12

An oinoloth from dnd

One of the more powerful yugoloth varieties is the oinoloth, wicked portents of plague and pestilence. Like many yugoloths, they serve as interplanar mercenaries. They use the blight that follows them wherever they go in service of the highest bidder.

In an interesting twist, oinoloths are just as cable of healing as they are of harming. They can remove conditions like paralyzed or poisoned at the steep cost of a creature's maximum hit points. This is a difficult prospect, but it might be a useful resource for a party who needs to cure some kind of powerful poison or disease.

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11 Beholder

CR: 1/2 - 14

Beholder attacks adventurers from DnD official art

Beholders are one of the most recognizable monsters in all of Dungeons and Dragons. They are most famous for their array of powerful eye beams, ranging from disintegration to heat to even petrification. But beholders are as smart as they are powerful.

A beholder can easily use its wits and minions to destroy its opponents without ever needing to fire an eye beam. A beholder that has made its lair in the Underdark is sure to be attended by all manner of other creatures, in addition to traps and hazards keeping it safe from any who might mean it harm.

10 Dire Troll

CR: 13

a dire troll in dungeons and dragons

While D&D's trolls are known for being voracious eaters, they rarely step over the line into cannibalism. When they do, however, their bodies undergo horrifying changes, turning them into dire trolls. A dire troll will graft parts of other trolls onto itself, giving them more arms, heads, and mouths.

Even more powerful than a normal troll, the dire troll's signature regeneration is only partially halted by acid and fire damage. This can make an encounter with a dire troll a potentially un-winnable scenario for parties without easy access to those damage types, potentially forcing them to flee deeper and deeper into the Underdark.

9 Neothelid

CR: 13

a neothelid monster in dungeons and dragons

Mind flayers begin life as small tadpoles and are eventually implanted in a humanoid's skull to mature into the humanoid form most D&D players are familiar with. However, when left alone, these tadpoles will resort to cannibalism until a final survivor stands. That survivor eventually becomes a giant neothelid, a horrid monstrosity hated even by other mind flayers.

Unlike their mind flayer brethren, neothelids are extremely unintelligent and blind. They seek out other creatures with one goal: to consume. Though they don’t have the same level of active psionic abilities, they do have some latent abilities like at-will levitation and several psychic-based ranged attacks.

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8 Elder Brains

CR: 14

An Elder Brain in DnD 5e

In the final stage of its life cycle, a mind flayer has a chance to become an elder brain. These horrid creatures rule over colonies of other mind flayers through a telepathic connection to their subjects. An elder brain can use several powerful spells to protect itself, including Levitate, Modify Memory, and Dominate Monster.

In addition to their own powers, elder brains are always surrounded by a colony of subordinates, so even drawing close to one will entail a full adventure in and of itself. Locating and destroying an elder brain could be an entire adventure or campaign in and of itself.

7 Nabassu

CR: 15

a dnd nabassu, a hunched dark winged demon

Nabassus are among the most powerful demons in D&D and are perfectly at home in the depths of the Underdark. These creatures have an insatiable appetite for humanoid souls and can devour them to restore their hit points and enhance their attacks.

Nabassus can also drain a creature's soul with a single look, dealing massive amounts of damage and potentially killing the target outright to later raise them as a ghoul. A high-level party traveling the Underdark in places known to have connections to the Abyss could be at risk of a nabassu attack at any time.

6 Purple Worm

CR: 15

a purple worm in dungeons & dragons

The purple worm is a gargantuan worm covered in spikes and scales that serve as armor. Purple worms are another of the most iconic D&D Underdark monsters, leaving giant tunnels in the rock behind them as they burrow through solid stone.

Any adventurers unfortunate enough to find themselves fighting a purple worm are at risk of being swallowed whole, a fate only slightly worse than being struck with the worm's venomous tail stinger. Purple worms are perfect for high level D&D parties who might be a bit too comfortable with their place in the food chain.

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5 Nagpa

CR: 17

a nagpa monster in dungeons and dragons

The nagpa were once humanoid wizards, but were cursed by the Raven Queen to become ugly, bird-like monstrosities. There are only thirteen of these creatures left in existence, making them perfect end-game bosses for any Underdark D&D campaign.

A nagpa's magical ability to sway people means they can be behind any number of political machinations, and players might chase a nagpa to the Underdark after uncovering their schemes in the surface world. When cornered, they are more than capable of fending for themselves in combat with spells and an inherent paralyzing effect.

4 Drow Matron Mother

CR: 20

a drow matron mother in dungeons and dragons

These priestesses of Lolth might seem to be regular drow, but their power has boosted them to the heads of their houses and civilizations. A drow matron mother embodies the darkness and evil of the church of Lolth while maintaining control over vast networks of lower beings.

Matron mothers are also incredible spellcasters, able to conjure gouts of divine flame, open planar gates, and dominate the minds of others. While they are extremely powerful, they are at the mercy of a fickle god who regularly gives and takes powers for fun.

3 Shadow Dragon

CR: Varies

a dungeons and dragons Shadow Dragon ready to attack

A shadow dragon is a truly evil creature that was either born in the Shadowfell or was transformed by its darkness. They have all the power of a dragon, enhanced even further by the dark energies of the Shadowfell. Any dragon can become a shadow dragon, and doing so grants a suite of new abilities.

Shadow dragons gain improved stealth abilities, as well as an affinity for necrotic damage. A dragon is already a fearsome enough foe, but encountering one that can vanish into the darkness of the Underdark with ease is even more of a terrifying prospect.

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2 Nightwalker

CR: 20

The Silhouette of a Nightwalker in DnD

When a creature enters D&D's Negative Plane, there is a chance that a Nightwalker will cross over to take its place. The being cannot escape the plane unless the Nightwalker returns, which they rarely, if ever, do.

Nightwalkers are purely anti-life, sucking the living energy out of anything they can. They can permanently kill any person without effort. A D&D party at the end of their campaign might find themselves face to face with this creature in the depths of the Underdark, making for a truly climactic showdown.

1 Illithilich

CR: 22

A Mind Flayer using psionic powers on a creature in DnD

Though most mind flayers eschew arcane magic in favor of their innate psionics, some choose to break this taboo in pursuit of even greater power. Some of the most powerful even seek out undeath for themselves, becoming powerful illithiliches.

These creatures, known as illithiliches, combine the best features of both mind flayers and liches. They are able to stun opponents with psionic blasts, conjure clouds of poisonous gases, and even kill with a single word. Illithiliches also gain lair actions, which they can use to regain spell slots, transfer damage to enemies, and even call forth the spirits of the dead.