Quests for treasures and riches often send adventurers below the earth into realms uncharted against monsters unseen. Whether you’re visiting the delightful jeweled cities of the svirfneblin or breaking into an ancient liche’s tomb, you’ll want encounters to fill them. These tables are here to provide you with inspiration or random encounters to drop on your players and add some more life to the underground environments in your worlds!
Sources
Each encounter focuses on a monster from throughout the D&D 5e library; to see what book or source they come from, you can consult the Book column. The sources unabbreviated sources are Basic Rules (BR), Monster Manual (MM), Mordenkainen Presents: Monsters of the Multiverse (MPMM), Icewind Dale: Rime of the Frostmaiden (RoF), Out of the Abyss (OoA), Volo’s Guide to Monsters (VGM), and Storm King’s Thunder (SKT).
Underground Random Encounters
The following table provides random encounters for parties playing in various “tiers” of gameplay; they generally reflect encounters you can sculpt to work for tables within a level range. The Low-tier can work for levels 1-4, Mid-tier for levels 5-11, and the Upper-tier for levels 12+.
Low-Tier Adventuering Random Encounter Table
| d20 | Book | Encounter |
|---|---|---|
| 1 | BR | 1d6+3 giant fire beetles performing their daily foraging routines |
| 2 | BR | 1d4+3 shriekers growing from the walls and floor |
| 3 | BR | 1d6+1 green flumphs examining the plant life in an underground aquifer |
| 4 | MPMM | 1d4+2 neogi hatchlings returning to their hive with scavenged food |
| 5 | VGM | 1d4+1 xvarts and a xvart speaker performing an archaic ritual around a rock |
| 6 | MPMM | A herd of 1d4+3 deep rothes grazing on curious fungus |
| 7 | MPMM | 1d4+2 derro prepared to ambush a drow and their giant bat companion |
| 8 | BR | A scouting group of two drow and their giant lizard mounts |
| 9 | BR | 1d4+1 grimlocks wrestling with a giant poisonous snake |
| 10 | BR | An aggravated nest of 1d6+3 giant centipedes swarming from the walls |
| 11 | BR | 1d4+1 kuo-toa and a kuo-tao whip collecting glowing rocks in the damp dark |
| 12 | MM | 1d4+2 troglodytes tracking a demon that breached their territory |
| 13 | MPMM | Two chitine and their 1d4+1 giant wolf spider pets weaving a nightmare web |
| 14 | MPMM | A darkling elder and 1d6 darklings on an expedition to trade |
| 15 | BR | Three lurking darkmantles prepared to drop on unsuspecting passersby |
| 16 | MPMM | A gazer fleeing 1d4+3 deep gnomes chasing it from their home |
| 17 | BR | 1d4+1 magma mephits relaxing in a heat vent releasing hot gas to the surface |
| 18 | MM | A myconid adults and sovereign cultivating 1d4 violet fungus |
| 19 | MPMM | A duergar soulblade and two duergar seeking a rare weapon lost to them |
| 20 | MPMM | 1d4+2 screaming vargouille flying through the underground |
Mid-Tier Adventuring Random Encounter Table
| d20 | Book | Encounter |
|---|---|---|
| 1 | BR | Three gelatinous cubes clogging two passageways |
| 2 | BR | 1d4 gibbering mouthers rabbidly gibbering at each other over corpses |
| 3 | MM | 1d4+2 intellect devourers lost from their mind flayer master’s colony |
| 4 | MM | A nothic, minotaur skeleton, and quaggoth who’ve escaped mind control |
| 5 | MPMM | Two cave fishers and 1d4+2 piercers sharing prey |
| 6 | MPMM | Two choldriths and their 1d4+2 giant spider in the webbed ruins of a drow city |
| 7 | MPMM | A flail snail being corralled by 1d4+1 derro savants |
| 8 | MM | Two grek and two grell living in a destroyed duergar outpost |
| 9 | MM | A hook horror cornered by 1d4+3 drow hunters fighting to take it down |
| 10 | BR | A trio of spectators guarding an abandoned cache of magic items |
| 11 | BR | Black pudding resting in a pool before a staircase rising into a demonic temple |
| 12 | MM | A bone naga and 1d6+2 skeleton cultists tasked to maintain a yuan-ti shrine |
| 13 | BR | 1d4+2 flame skulls floating around their creator’s tomb |
| 14 | MM | An earth elemental and 1d4+3 symbiotic mud mephits breaking an outpost |
| 15 | MPMM | A mindwitness scouting for its mind flayer overlord |
| 16 | BR | An otyugh and roper who share a hunting ground |
| 17 | MM | A wraith and 1d6+4 shadows stalking the tomb that killed their living forms |
| 18 | BR | Two xorn guiding 1d4+3 dwarf bandits to a hidden trove of treasure |
| 19 | FTD | A young deep dragon and 1d6+4 grey-scaled kobold worshippers |
| 20 | BR | A drider and 1d4+3 drow warriors journey to uncover a dark relic |
Upper-Tier Adventuring Random Encounter Table
| d12 | Book | Encounter |
|---|---|---|
| 1 | MM | Two mind flayer arcanists and their 1d6+3 qugoth searching for their ship |
| 2 | SKT | 1d4+3 stone giants preparing an invasion of the surface world |
| 3 | MPMM | An ulitharid and three mind flayers planting larva into new hosts |
| 4 | BR | An aboleth and its 3d6+6 kuo-tao servants harvesting a black dragon’s bile |
| 5 | BR | Two behir carving out a larger cavern with lightning |
| 6 | MM | Two dao and their earth elemental pack mule moving elemental luxury goods |
| 7 | MM | A beholder and its four spectator guards refitting a city they stole from gnomes |
| 8 | MPMM | A neothelid and two mindwitnesses created to defend the hive |
| 9 | MM | A death tyrant and 1d4+2 minotaur skeletons digging for an ancient artifact |
| 10 | MM | A young red shadow dragon and its 1d4+3 black guard drakes hunting |
| 11 | MPMM | An elder brain, ulitharid, and neothelid plotting a takeover of the plane |
| 12 | BR | A rogue purple worm minding its own business |
