Yharnam Sewers Skill Challenge

Running a 5e conversion of the 2nd edition adventure “A Darkness Gathering” – a campaign I have just called Thoughts of Darkness (heavily inspired by Bloodborne).  Its tuned to level 14 characters and my party is made up of 6 to 8 PCs.  

The players used the following skill challenge to navigate the sewers and find the phthisic. In my game they never failed once – they got 8 successes straight up – so I never used the linked encounters except for the phthisic one. Oh well. PCs always running the DM’s fun.


You enter one of the many tunnels that run below the city, your eyes wide for any clues or trails that can lead you more easily to your goal. Bits of stone and masonry litter every surface and tiny spiders with various deformities or strange glowing bodies crawl through the shadows.

Setup: The PCs must make their way below the city to find the Durgan, Johanna’s missing brother.

Level: 14.

Complexity: 3 (requires 8 successes before 4 failures) if they enter via the sewer grate near Durgan’s home.  Complexity 4 if they use any other grates (12 successes before 5 failures).  Each success and failure counts as an hour of searching.

Group Skill Challenge: Multiply the DC by the number of PCs. All characters roll and must meet the group DC for a success.

Primary Skills: Perception, Investigation, and Survival. Each skill must be used at least once and then any skill combination can be used to complete the challenge except where noted otherwise.

  • Perception (20, Group check): You try to follow twists and turns, looking for clues in this confusing mess of tunnels.
  • Investigation (21, Group check, 4 Success Maximum): You use your skills of investigation to find clues which would indicate you are heading in the right direction. Each success increases the DC by 1. See area “G. Pipe Junction” for details.
  • Survival (15, Group check): The use of tracking is the most effective way to find the phthisic lair.

Special: If the PCs are accompanied by Johanna they have +2 to all their rolls. Also, each failure results in an encounter. See the encounter section below. Finally, the sewers are considered difficult terrain for the most part as the PCs are trudging through water or sludge to make progress. For each hour beyond 8, the characters explore apply the forced march rules (DC 10+1 CON for each hour above 8 or suffer 1 level of exhaustion).

Success: PCs discover the phthisic lair – Testament of the Mind – managing to either avoid or overwhelm any encounters along the way.  However, they have at least one encounter as they traverse the sewers.

Failure: The PCs go off track and run into the phthisic. Once PCs deal with the phthisic, they can attempt the skill challenge again to discover the creature lair. The characters may retain the successes they already have gained for the next attempt (this assumes they can always trace their footsteps back and are mapping).

Encounters: Venturing below the city while seeking the missing person could lead to several encounters. Roll on the table below, each encounter should occur once before repeating any, except for number 8.  The phthisic can be encountered multiple times by the PCs before they get to the Testament of the Mind.

  1. Black Pudding. See area “F: Blackpool.” (This is an elder black pudding identical to a standard pudding except that it is huge sized and has maximum hit points. It can also attack with acid sharpened bone spears it pushes out from its body turning it pseudopod damage into piercing damage if it so chooses).
  2. Cranium Rats. The rats are actually allies of Ebrietes, Son of the Cosmos (Strom from the original) and are trying to help the party but will not make contact. The swarm allied with Ebrietes is known as UNITY. They will provide some benefit depending on what is needed, like allowing the characters to have an automatic success by following a rat down a tunnel.
  3. Winter Lanterns. The winter lanterns scour the tunnels for food. They use stealth to pull characters into a junctions ceiling area.  They then trigger their singing.
  4. Neo-Otyugh. See area “H: Inhabited Pipe Junction.”
  5. 1d4 pockets of sewer Vampiric Mist – see area “I: Tangled Junction”.
  6. Gas Pocket – see area “E. Gas Pocket.”
  7. Outlet – see area “D. Outlet”.
  8. Phthisic. The phthisic attacks and once it dies it dissolves into mist leaving no corpse behind.  It reappears in its lair and starts regenerating.