D&D 5eGM Resources

Monthly Encounter #13: The Corrupted Underwater Dragon (lvls 1-4)

Thumbnail art from Josh Benson

Here at Tribality, we’ve decided to provide our readers with Encounters ready to be added to your table. I’ll be creating new ones monthly for you to have a big collection to look through when you run out of ideas for your game. If people end up liking them we may start releasing them in easy to print PDF format.

Don’t forget to comment feedback or possible variations for others to see and/or possibly implement when running this encounter. Without further ado, hope you enjoy it:

Setting: Agnostic
Location: Hamlet near a lake
Lvls: 1-4

Encounter background

Ginya Skullhead is a  sea hag that wanted no more than to cause despair to the citizens of Musharb, a small fishing hamlet bordering a lake that depends on the day to day catch to survive. Ginya encountered a small bronze dragon wyrmling named Estirmatuxz trying to create its own lair below the waters. The beauty in its bronze scales was enough to cause her fury. She cursed the creature, causing it to kill any fish the dragon saw, as well as having it come out of its lair once per day to kill more fishes.

The Corrupted Underwater Dragon

Adventure Hook

The players could have been informed about this hamlet’s problem in a variety of ways:

  • A character with the sailor background was one of the fishermen affected by the fishing decrease, or they might have seen some lights underwater when fishing.
  • A merchant from a near city or town tasked the player character to find out why Musharb was not exporting the usual catch from the day.
  • The character finds a poster on a tavern or guild that indicates the people from Musharb will reward those who solve the strange happenings going on.
  • The player character receives a letter from a friend or family member that knows them to be an adventurer. It’s a plead for help.
  • The adventurers travel near the lake and see flashes of yellow light in it. If this is the case you may skip the Musharb section.


When the PCs reach Musharb, one of its citizens in the streets runs into a house. Moments later, a well kept human woman with a straw hat comes out and greets the adventurers, asking them to enter her home. This person is Matilda Laurette, the hamlet’s only medic and the one who speaks for Musharb. She pronounces the letter “s” as an “h” and accentuates the letter “t” when she talks. Matilda provides the following information to the player characters:

  • For the last week, fishes have been reported dead floating on the water.
  • The amount of dead fishes is way too high each day for the fishermen to gather and this high death rate means they will be shortly left with no fish to collect.
  • The fishes are found roasted on the waters.
  • Thomas the fisherman said he saw two days ago some lights coming from underwater.
  • At first, the people from the hamlet thought some individual could have been doing this to mess with them, but Thomas’s report confirms otherwise.
  • Matilda sent an adventurer the day before to investigate the waters. No one has heard from him since.
  • The adventurers need to find what is causing it and solve the problem.

Matilda promises to give the adventurers 30gp each for the task. They must bring something that demonstrates the problem is solved.

Adjusting the encounter: If the characters are lvl 1 or 2, have Matilda give each of the characters a potion of water breathing the hamlet bought with their founds.

The lake

Taking the time to investigate the lake borders takes about 2 hours. The only thing left around it is a fishing rod on the ground. If night time approaches, the adventurers have a 50% chance of seeing a light on one section of the lake with a successful DC13 Wisdom (Perception) check. Shortly after, roasted dead fishes appear over the water. If the PCs manage to get closer in a quick manner, they see a metallic shine moving towards the east (the dragon’s lair).

Submerging under the lake makes it hard to see. Wisdom (Perception) and Intelligence (Investigation) checks are made at disadvantage while underwater. In order to find any track leading to what may have caused the trouble, PCs will need to do a DC13 Wisdom (Perception) or Intelligence (Investigation) check.

  • On success, the PCs find an underwater cavern after 1d4 hours of search. This cavern has spears placed facing upwards all around the entrance. Proceed to Dragon’s Lair.
  • On a failure, the PCs spend 1d4 hours searching but find no more than some dead fishes floating on the surface. This might mean they are closer to the answer, but there’s no way to be sure. 1d4-1 (minimum of 1) sahuagineach mounted on a skeletal undead giant sea horse appear and confront the PCs. The skeletal undead giant sea horses attempt to escape when the sahuagins are defeated. The players get to make the DC13 Wisdom (Perception) or Intelligence (Investigation) check again. On a failure again, repeat this encounter rerolling the number of enemies. Defeating them leads them to find the Dragon’s Lair
    • Skeletal Undead Giant Sea Horse: uses the giant sea horse stat block, with the following changes:
      • Type is changed to undead.
      • The creature is vulnerable to bludgeoning attacks.
      • The creature is immune to necrotic and poison damage.

Adjusting the encounter: If the characters are lvl 1 or 2, the sahuagin appear damaged and have 14hp each.

Note: Allow the PCs to do a peaceful short rest out of the lake if needed. Low-level adventurers can die easily and we don’t want them to reach the final fight very damaged. If they want to do a long rest remind them that time is of the essence. The longer the player characters take in solving these fishes will keep on dying and Musharb may lose its only profiting activity.

The Dragon’s Lair

Light: The cave interior is lightly obscured, only illuminated from little holes in the ceiling  from which the sunlight or moonlight comes through.
Spears: The spears are stuck on the walls dealing 1d8 damage to those pushed against it.

No matter if the PCs enter through the right side, the left one or both, read the following text aloud:

The surprising sound of a sneeze echoes through the cave, accompanied by the sound of crackling electricity. The sound comes from the center of the room, where a bronze scaled dragon with obscure black eyes floats. From its position, one of the three sahuagin in the room is launched by the sneeze towards a spear filled wall. The sahuagin dies impaled as all creatures in the room turn their gaze towards you.


(Includes ungridded versions for VTTs)

After the sahuagin’s death the room is occupied by 2 sahuagin and a cursed bronze dragon wyrmling. The sahuagin work for Ginya but know not of her location. Only Estirmatuxz knows (the wyrmling). These creatures were ordered to annihilate those who dare enter the lair. However, if anyone was to fight hard enough that adventurer should be left unconscious as Ginya has plans for them. A remove curse spell on Estirmatuxz will return it back to normal, making it change sides to help the PCs.

Note: The boxed text was added to show the players that they can use the spears to their advantage. If they somehow manage to have the dragon push the sahuagin against the spears with its Repulsion Breath have the sahuagin get impaled and killed from it, no matter how good on health they are. Managing to do this should feel like a reward.

Cursed bronze dragon wyrmling: Uses the bronze dragon wyrmling stat block with the following changes:

  • The dragon has 40hp
  • The Lightning Breath deals 22 (4d10) damage on a failed save, half on a success.

Adjusting the encounter: If the PCs are:

  • Lvl1: Replace cursed bronze dragon wyrmling for bronze dragon wyrmling, and the sahuagins have 16hp.
  • Lvl 2: Replace cursed bronze dragon wyrmling for bronze dragon wyrmling

Treasure: A skeleton is impaled on one of the spikes, still wearing some damaged clothes. It has 2 potions of healing and boots of elvenkind on its feet. This corpse belonged to the adventurer that was sent the day before.

Additional information

  • A PC can breathe an amount of time underwater equals to 1 plus their Con modifier (suffocating)
  • PCs move at half speed unless they have a swimming speed.
  • Take into account that casters start suffocating if they can’t breathe water and cast a spell with a verbal component. This doesn’t appear in the PHB but can be found in a Sage Advice by Jeremy Crawford.

Want more encounters?

If you liked this encounter and would like to see more check out the index I created with all the monthly encounters I’ve created so far, listed by tier lvl and environment: