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The Underdark is home to some of the most influential creatures of Dungeons and Dragons lore. The brain-eating mind flayers and all-powerful beholders claim this area as their home along with the drow and 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 subterraneon 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, with the very terrain itself being hostile. Any creature at home in the Underdark will be made even more powerful when used in conjunction with twisting tunnels, dangerous chasms, and hazards like toxic fungi or rockslides. All these factors can help an Underdark creature present a threat beyond what its challenge rating might suggest.
Updated by Declan Lowthian on June 6, 2022: The Underdark is home to countless creatures, and while many of these are very high level, there are foes suited for lower-level D&D characters as well. This list has been updated to include a wider variety of Underdark denizens for use at all stages of a campaign.
15 Umber Hulks Cause Confusion With Their Gaze
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 straightforwart-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. 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 course of action. These creatures can tunnel through solid rock, so an Underdark-themed D&D campaign could feature an umber hulk ambush at any time, forcing the players to stay on their toes.
14 Cloakers Are A Classic Dungeon Denizen
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 attamps to suffocate its prey by engulfing them. Cloakers also emit a dreadful moan that can inflict fear on 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 Serve A Mysterious Master
Once elves who worshipped the Raven Queen, the shadar-kai now reside in the dark plane of the Shadowfell. Most of them 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, able to 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 Oinoloths Bring And Banish Plagues
Yugoloths are a type of fiend divided into castes. One of the more powerful yugoloth varieties is the oinoloth, wicked portents of plague and pestilence. Like many yugoloths, they serve as inter-planar mercenaries, using the blight that follows them wherever they go in service of the highest bidder.These creatures are the harbingers of pestilence and control plagues. In an interesting twist, oinoloths are just as cable of healing as they are of harming. Their healing comes at the cost of a creature’s maximum hit points, but it might be a useful resource for a party who needs to cure some kind of powerful poison or disease.
11 Beholders Are A D&D Staple
One of the most recognizable monsters in all of Dungeons and Dragons, beholders are famous for their array of powerful eye beams, ranging from disintigration to heat to even petrification. Beholders are as smart as they are powerful, using their wits to destroy any who oppose them before needing to use their eyes. 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 Trolls Are Worse Than Trolls In Every Way
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, their 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 Neothelids Are Malformed Mind Flayers
Mind flayers begin life as small tadpoles, eventually implanted in a humanoid’s skull and maturing into the humanoid form most D&D players are familiar with. However, when left alone, these creatures will resort to cannibalism until the final survivor stands. The survivor becomes the giant neothelid.
Unlike their mind flayer brethren, these creatures 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 mental attacks.
8 Elder Brains Rule Over Mind Flayers
In the final stage of its life cycle, a mind flayer may 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.
7 Nabassus Are Hungry Demons
Among the most powerful demons in D&D, nabassus are at home in the darkness 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. They can also drain a creature’s soul with a single look, dealing massive amounts of damage, potentially killing the target outright and raising 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 Worms Can Tunnel Through Stone
The purple worm is a gargantuan worm covered in spikes and scales that act as armor. They 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 is 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.
5 Nagpas Are Corrupted Wizards
The Nagpa are formerly humanoid wizards who were cursed by the Raven Queen to become ugly, bird-like monstrosities. While the Nagpa might look frail and weak, they are stronger than they look. They scheme towards the end of civilization through puppeteering and manipulation. If that fails, they are capable spellcasters in their own right.
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.
4 Drow Matron Mothers Lead Their People
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 takes and gives powers for fun.
3 Shadow Dragons Are Stealthy And Strong
A shadow dragon is a truly evil creature that was either born in the Shadowfell or was transformed by its darkness. The result is a monstrous creature with all the power of a dragon, enhanced 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 encoutering one that can vanish into the darkness of the Underdark with ease is even more of a terrifying prospect.
2 Nightwalkers Embody Death Itself
A Nightwalker is created when a being enters the Negative Plane, essentially trading places with it. The being cannot escape the plane unless the Nightwalker returns, which they rarely, if ever, do. These creatures 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’s journey might find themselves face to face with this creature in the depths of the Underdark, making for a truly climactic showdown.
1 Illithiliches Use Arcane And Psionic Magic
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 combine the best features of both mind flayers and liches, able to stun creatures with psionic blasts, conjure clouds of poisonous gases, and even kill with a single word. Powerful as they are, illithiliches also gain lair actions, which they can use to regain spell slots, transfer damage to enemies, and call forth the spirits of the dead.