TEXT: Written by Dimitri Lambermont & Remko van der Heul 
  Cover art by Wouter Florusse
  Nerdicted presents
  
  20 Disturbing Dungeon Encounters
  Twenty fun, scary and disturbing encounters you can throw at your party.
  Written by Dimitri Lambermont and Remko van der Heul
  Artwork by Wouter Florusse
  
  20 disturbing dungeon encounters
  W
  hat lurks in the deep and dark dungeons?
  What horrors wait for you? Will you ever get
  out from under the mountain again? Below
  you will find 20 fun encounters you can use
  at any time your party ventures
  underground. 
  Encounter 1
  You are asked to enter an old cave in the nearby mountain.
  It is known that the cave houses an ancient cloister.
  Pilgrims have gone there and have never returned. You are
  asked to investigate the recent disappearance of a group of
  acolytes. A local rumor tells that the cloister is cursed. The
  curse actually exists and is that all spells you cast will
  become literal versions. 
  For example: the spell burning hands causes your hands to
  grow so hot you get burn wounds.
  Encounter 2
  You are deep, deep inside a dungeon. The party is either
  lost or seeking something. You come upon a large room at
  the end of a tunnel with a lot of stalagmites. One seems
  curious. In the rock you see a strange tiny creature that
  appears melted into the stalagmite. It is an odd scary
  devilish creature. You make out it is an Imp. 
  The party needs to move past the imp to move to the exit of
  the room. If they do so the first PC that passes it hears a
  voice in its head:
  “Please help me escape this trap. I can help you find what
  you seek. I don’t want to be stuck here forever. My name is
  Brimward and I am an Imp. I would serve you for two years
  if you free me.”
  Encounter 3
  The party rogue uncovers a trap in the hallway. In the floor
  just in front of them is a revolving trapdoor. If stepped on it
  will flip with no more pressure than a soft push. The floor
  parts will reach up to the ceiling if sprung and there is no
  way to jump past the pit.
  The other side is trapped with a secondary trap (invisible
  force wall). If jumped before the trap is sprung the PC
  doing so is flung back onto the revolving trap door,
  triggering it. The PC then falls down 30 feet in a pit filled
  with acid...
  Encounter 4
  Needing to move on in a cavernous dungeon the party
  enters a cave. On one side the cave is filled with a
  seemingly shallow five feet deep pool of water. This water
  takes up about 80-85% of the cavern. There are nearly 100
  stalactites and stalagmites all over the room, water drips
  down and you hear it echo as it hits the pool or a stone
  surface.
  Unbeknown by the party, hidden among these stalactites is
  a sizeable colony of Darkmantles. In the pool of fairly clear
  water lay the remains of former adventures that fell prey to
  this colony. The party must be very silent to pass unnoticed.
  A single loud sound and the colony wakes up and will
  descent upon the party to devour them. In the pool lies
  among others the remains of a dwarf (rogue) still wearing
  an intact leather armor.
  Encounter 5
  Entering an underground tomb the party moves forward
  through cobwebs and swirling dust. Reaching the end of
  the tunnel the floor just gives way (a trap). The party slides
  down, landing chin deep in dark, smelly and thick muddy
  water. Trying to wade through the deep dirt toward a rocky
  ledge one of the PC’s feels something touching his leg. And
  then the party notices movement. Hardly able to move the
  party needs to escape the clutches of the Otyugh in its lair.
  Encounter 6
  Miners from a nearby community discover a preexisting
  passage that leads deep underground. The PCs are hired to
  explore the cavern and see where it leads. Strange plants
  cover the path before you. They glow with an eerie
  phosphorescence.
  Nature skill check (DC 20). A trained PC can identify the
  plants. You know that they are indigenous to caverns like
  this and that touching them, or walking over them, will
  result in spores being ejected into the air. Inhaling the
  spores will make the PCs sick. 
  With this knowledge the party can safely navigate
  (perception check) the plants. If not they will get the chance
  to be poisoned. A successful Medicine check lets poisoned
  characters make one save to regain the lost hp. If your
  Medicine check succeed by 5 or more you provide a +2
  bonus to the save. 
  Next up a sinkhole 15 feet wide has formed in the path
  before you. There is no way around. Skill with rope is
  needed to be able to swing across it. After one makes it
  across a safety line can be realized and the journey can
  continue.
  The party comes upon an area where rocks sharp as knives
  jut out from the walls, floor and ceiling. Careful navigation
  is needed to avoid wicked scratches to move across this
  part of the tunnel as the party moves further and further
  underground. 
  A collapsed part of the tunnel blocks progress. A dwarf
  or skilled adventurer is able to discern that with moving a
  few larger boulders passage could continue needing skilled
  magic or just plain manual strength to move the stones
  (Athletics) 
  2
  
  From the main passage many side passages now run. It is
  getting harder not to lose direction, but tracks of recent
  passage by unknown creatures keeps the party on the right
  track. With stealth (DC15) the creatures can be avoided
  and at the end of the tunnel lies a treasure horde. Without
  stealth the creatures might stir and the party is in for a fight
  before reaching the treasure.
  Encounter 7
  You are sent on a diplomatic mission to a local band of
  dwarves in the nearby mountains. The dwarven chieftain is
  old, grumpy and very impatient. And he only talks in
  whispers. You have a hard time understanding what he
  says anyway through his thick dwarven accent.
  If you somehow do not anger him. he agrees to do what you
  have requested. If you do him one favor. Part of the mining
  complex was recently destroyed by a mysterious
  earthquake and he asks you to investigate this first.
  Encounter 8
  You are deep in the dark tunnels under the mountain. In
  the distance you hear the faint murmur of a waterfall.
  Through the echoing noise of the waterfall, you hear a
  magical melody. One voice begins, then another chimes in.
  Then another. Soon there is what seems like a choir
  chanting. 
  DC11 saving throw or be charmed. Charmed: a charmed
  creature can't attack the charmer or target the charmer
  with harmful abilities or magical effects. The charmer has
  advantage on any ability check to interact socially with the
  creature.
  If the adventurers walk into the room proper they see an
  area that appears open somewhere high above their heads.
  A waterfall is falling into a pool of clean and cold water.
  Within the pool (D20) harpies are taking a bath and
  singing. Upon seeing the heroes come in they scream and
  attack.
  Encounter 9
  You are sent to investigate the disappearance of a lot of
  people (about 200) from a large mining town. They have
  been captured at least 6 months ago. As you make your
  way through the maze you find several corpses strewn
  across the many rooms. These [insert monster] have been
  battered to death and torn asunder. All doors of the cells
  are open. Every room is a mess. There are scribblings on
  the walls in feces and blood. Here and there you also find a
  corpse of a human. They look mangled and starved. 
  It appears all the monsters that ruled this complex have
  been killed. You hear the echoes of cries and howls,
  unintelligent gibbering coming from the distance.
  That is when the first attack comes. You are assaulted by
  (D20) humans. They have all clearly gone quite insane from
  being stuck in the darkness so long. The deeper inside you
  venture the more scenes of depravity attack your senses.
  Encounter 10
  All these hours underground you have heard a dripping
  sound echoing through the tunnel and have followed it. The
  constant dripping nearly drove you mad. There also is a
  strong metallic smell in the air. 
  Coming from the dark tunnels you stumble into a large
  open cavern. The cavern is a perfect circle and its walls are
  pitch black, hard obsidian stone. In the middle of the room
  stands a perfect round pool also made of black stone.
  Intricate signs adorn it. The light of your torches does not
  reach the highest points of the caverns disappearing into
  the shadows. 
  If the players decide to walk towards the pool they walk
  through a slight drizzle of drops. Upon investigation, they
  discover the drops are red. That is when they hear a low
  deep moan coming from the darkness above. Then another.
  Bringing a light source higher up unveils about 20 hill
  giants hung up head down from the ceiling and bleeding
  from many small puncture wounds. Who would do this?
  Encounter 11
  As you walk through the tunnels deep in the earth you hear
  a low rumble. The whole place around you shakes. Nothing
  comes down from the ceiling, only some dust. You do see
  cracks appearing here and there. But the structure appears
  to be safe.
  What the earthquake did do. was release a combination of
  natural gasses, which are spreading through the tunnel
  system. Although the mix of gasses is not harmful, it does
  cause hallucinations. DC15 Wisdom Save to keep your
  wits together. On a failed save roll a D20 for hallucination
  effects. 
  Hallucination Effects
  Roll Effect
  1 -
  4
  Hear voices. You may sense that sounds are coming
  from inside or outside your mind. You might hear
  voices talking to each other or feel like they're
  telling you to do something.
  5 -
  9
  See things. For example, you might see insects
  crawling on your hand or on the face of someone
  you know.
  10
  -
  14
  Smell things. You may think an odor is coming from
  something around you, or that it's coming from
  your own body.
  15-
  19
  Feel things. It might seem to you that you're being
  tickled even when no one else is around, or you
  may have a sense that insects are crawling on or
  under your skin.
  20: Extreme Paranoia and Hysteria. You run in fear to
  the nearest exit.
  3
  
  Encounter 12
  You come across a large hallway in the dungeon. It ends in
  a large domed structure. Almost like a temple was built
  inside the mountain. The temple feels ancient. Like it has
  been here for ages. On each wall of this temple are several
  painted scenes. As you make your way around you begin to
  notice that these paintings look awfully familiar. They
  speak of your past endeavors. Only you are shown as the
  antagonists. As devils. You are slaughtering the innocents
  and stealing all their treasure.
  In every picture, there is a heroic figure looking on in
  disdain. On the final panel, you see an underground temple
  with you inside it. The 'hero' is depicted as an angel. You
  are depicted as dead at his feet. That is when a door behind
  you opens.
  Encounter 13
  While entering a dungeon after about half a mile following
  the one long passage slightly down you come upon a
  crossroad, stepping forward to take either of the 3
  passages, you feel a slight feeling of vertigo. After
  continuing your way you notice light in the distance only to
  discover that you are right back where you started. DC15
  Perception to find a hidden door that takes the party out of
  this loop.
  Encounter 14
  The party is exploring an abandoned mine, while they
  move deeper and deeper in the mine they come upon a side
  passage that’s been bolted closed with thick wooden
  boards. If the PC’s decide to remove the boards they
  unleash a (horde) of (D20) undead skeletons that have been
  captured behind the wooden planking.
  Encounter 15
  The section of the dungeon the party stumbles upon is an
  area that amplifies sound 20 fold. The player sneaking in
  first hears footsteps from the room, and whispers almost
  seem like normal speech echoing through the cavernous
  space. Lookouts lie in wait for adventurers entering this
  cave of echoes. They get an early warning to spring the
  ambush they have planned. Any normal to loud noises
  cause the PC’s to be deafened. 
  Safe DC 12 or be deafened. A deafened creature can't hear
  and automatically fails any ability check that requires
  hearing.
  Encounter 16
  As you move forward the temperature drops every five
  miles. It becomes chilly and then cold. As you round the
  corner you enter the first of a complex of ice caves. Snow
  covers the ground here and the walls are blue with ice.
  There are myriad chambers that all interconnect and cold
  air flows through them. At the end, you find a large cavern.
  In it are large tombs. You have found the burial grounds of
  Ice Giants. 
  Variant: Salt crystals forming, ending in a huge salt cave,
  filled with spiders made of crystalline / salt.
  Encounter 17
  You enter a huge cavern. The cavern has been hewn from
  the stone of the mountain. After looking around you find
  you are inside an underground temple. Everything here is
  giant sized. The symbol of the stalactite adorns the walls
  and seats. The room is beautifully decorated. 
  Religion check (DC10) shows you are in the temple of
  Skoreaus Stonebones - God of stone giants and crafts. At
  the far left of the temple you find a huge statue of
  Skoreaus. The room is adorned with stone statues. If the
  adventurers take anything a stone giant statue comes alive
  and attack.
  Encounter 18
  You are walking through a tunnel with the sound of rushing
  water coming ever closer. At the end of the tunnel you
  arrive at a small landing. The road splits. One path going
  left, one right. The path is several feet above a wild rushing
  underground river. The path is five feet wide forcing you to
  walk single file. The right path goes on several miles but
  ends against a wall, the water rushing on through a small
  opening. The left path leads to an underground lake. Both
  paths force the party to walk single file. The path is slippery
  and requires a (DC10) Dexterity check. Random creatures
  can attack from above.
  Encounter 19
  Your journey ends in a cave. There does not appear to be
  any way out. On the wall are ancient texts in a script
  resembling common but in an older form. Deciphering it
  requires a Wisdom check (DC15). Upon speaking the right
  words a ghostly figure appears. A spectral Dragonborn
  Wizard who acts as guardian of the Room of Truth beyond.
  Only those of good alignment may pass, one at a time.
  Inside the room each adventurer receives a vision of their
  true nature. DM can insert personalized plot hooks here.
  Those who try to trick the Dragonborn Guardian will
  receive horrible visions.
  Encounter 20
  You find a large steel plate in the floor. It appears locked.
  Opening it is easy. Below the plate you find a large round
  shaft with metal bars offering you stairs downward. You
  descent down the shaft for 100 feet. At the bottom you
  enter a large cavern. Inside it you find a huge stone cloister.
  The doors are open. When entering the cloister you find a
  hall with 30 monks sitting perfectly still. Upon further
  inspection you find they are mummified monks. As you
  walk past them you discover some are still breathing. They
  have been sitting like this for the last 100 years. 25 are
  completely mummified. Five however are still alive.
  4
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/5th Edition (5e)/3rd Party/DMsGuild/Nerdicted Presents - 20 Disturbing Dungeon Encounters.pdf