Are your adventurers making the long descent down to the underdark? Have you adventurers stumbled upon a map that leads to a treasure buried deep in an underground cave? Here is a list of 10 Awesome Monsters for a Underground Encounter from the Dungeons & Dragons 5th Edition Monster Manual in alphabetical order.
Challenge Rating: 3 | p. 24
Basilisks turn their prey to stone, with their supernatural gaze, and them consume the stone. They can be trained, if raised in captivity from an egg. Have your adventurers face off against a basilisk and its master in an underground cave.
Challenge Rating: 11 | p. 25
Behirs lair in hard to reach locations such as deep pits, high caves in cliff walls. Have a behir attack from ambush in one of these locations, using the ceiling and walls to its advantage. For a social encounter, have a very full behir decide to aid your adventurers somehow on their way to face a powerful dragon.
Challenge Rating: 13 or 14 (in lair) | p. 26
These iconic floating spheroid aberrations dismiss all other creatures as lesser beings. Set a beholder in its lair where it gets access to ambient magic for an even greater challenge.
Challenge Rating: 6 | p. 120
Drow who have failed Lolth in some way can be turned into these twisted creatures of madness. Surround a drider with giant spiders (CR 1 | p. 328) for a tough random encounter in the Underdark. Add in some spellcasting abilities, if the drider was a spellcaster before being transformed into a monstrosity.
Challenge Rating: 8 | p. 41
Cloakers are usually found lurking alone in dungeons and caves. These stealthy aberrations are named for their resemblance to a dark leathery cloak. By the time a cloaker moves into attack and reveals its white underside, it will already be attacking with bite and tail. Cloakers also have a fear inducing moan and the ability to create illusory duplicates of itself. Have your adventurers interrupt a rare conclave of multiple cloakers for a tougher challenge.
Challenge Rating: 7 to 8 | p. 221-222
Mind Flayers are psionic tyrants and slavers usually found in the Underdark. They are magically resistant and are natural psionic spellcasters with the ability to detect thoughts, levitate, dominate monster and plane shift. Their abilities and lawful evil alignment make them naturals to create an empire on the backs of mind-controlled slaves. Also called illithids, they are the evil at the heart of many adventures. Bump up a Mind Flayer to a deviant Mind Flayer Arcanist for a higher challenge.
Challenge Rating: 3 | p. 223
Minotaurs have the ability to perfectly recall any path they have traveled and live to ambush your party as it enters the labyrinth. A minotaur cares little for tactics and will recklessly attack and charge, leaving itself open to counter attacks by those that survive the onslaught. Place one of these savage monstrosities at the center of a labyrinthine set of tunnels or some other maze-like environment.
Challenge Rating: 15 | p. 255
These massive monsters burrow and chew through solid rock in pursuit of its prey, which is anything it encounters. Purple worms are attracted to noise and can be used as a big surprise interruption for a higher level group fighting an easy battle. A purple worm (or multiple worms) can also be a source of a complex network of tunnels. Defeating a purple worm can be a good time for you to drop some serious treasure on your players as these worms are usually quite filled with precious metal and gemstones, especially if they are hunting in a mine.
Challenge Rating: 1/4 | p. 290
These savage and loathsome humanoids can be found in the shallow depths of the Underdark dwelling in filth. Nearly their entire existence is devoted to gathering food. Have a group of troglodytes hunting your lower level adventurers, looking to drag them back to their lair as food. Have any adventurers who are knocked unconscious in a battle dragged away to be be eaten unless rescued by those left standing.
Challenge Rating: 5 | p. 292
Looking for food, umber hulks will suddenly tunnel into a cave or burrow into the wall of a passage and wait for your adventurers to pass by. Umber hulks have a confusing gaze that can scramble the mind of those within 30′ that look at its eyes. Set an umber hulk at the center of a mystery of disappearing explorers or miners to set-up a tough encounter for lower level adventurers.
- Bat, Giant Bat & Swarm of Bats
- Carrion Crawler
- Deep Gnome (Svirfneblin)
- Dinosaurs – yes they survive deep in the earth
- Giant Spider
- Gibbering Mouther
- Intellect Devourer
- Hook Horror
- Myconid & Quaggoth Spore Servant
- Rust Monster
- Spirit Naga
- Violet Fungu