Mystery Index

Design Notes & Core Rules


  • BPRD: Plague of Frogs (comic) Re-Animator (film) Alien (film)


  • There has been a rash of attacks happening within the city, leaving victims on the precipice of transformation.
  • Dr. Shelly has been using her health clinic as a front to experiment on the houseless (using science and the occult) in order to try and restore an ancient precursor race of frog-monsters.
  • She has been releasing her failures into the tunnels where they continue to mutate and change. They begin practicing rituals from a time long since forgotten.
  • Dr. Shelly’s work has been accelerated by the recent acquisition of a rare text provided to her from a mysterious benefactor (The Archivist)

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Factions & Their Goals

  • Dr. Shelly: To bring about the second coming of the primordial humanoid frogs spoken of within Ogdoad’s Well.
  • Frog-Monsters: They are slowly becoming something new. Whispers from the Old Power’s drive them to propagate and start the Ritual of Incursion.
  • The Archivist: Used B&H deliveries to anonymously donate Ogdoad’s Well to Dr. Shelly. Interested in seeing what Dr. Shelly corruption will yield. He will add whatever results to his collection. Prefers to take indirect actions/use others to acquire items.
  • The Authorities: Choose an organization for your game that awaits off screen. They could be: A private company/ A secret government agency/ An ancient order… This group cares more about acquiring power and maintaining control than saving innocent lives.

Doom Clock

Actions taken by the investigators change the progression of the DOOM clock. The progression below is what would happen if investigators don’t intervene. Changes to the DOOM clock should consider the goals of the factions at play.

  • A rash of attacks by released Frog-Monsters. Victims go catatonic with bouts of delirium.
  • A Frog-Monster ascends to priesthood, creating a shrine of flesh and bone to the Old Powers.
  • Survivors of the attacks turn into frog-monsters over a single evening.
  • Images of frog-monsters picked up by the media.
  • A congregation of frog-monsters overtake the lab, taking Dr. Shelly and the tome to the flesh chapel.
  • Frog-monsters complete the Ritual of Incursion - Dr. Shelly is the vessel.
  • The Authorities (see factions) come in to control the situation through force and acquire assets. The party will be targeted for its involvement. Massive casualties.

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Below are potential hooks for your party. Make sure that the hook makes sense for the group (align it to the Party Questions)

  • The party witnesses and is forced to intercede in a frog-monster attacking someone. Direct stress through contact with the paranatural.
  • The Archivist (either directly or anonymously) asks the group to look into the attacks or offers payment for any evidence of the para-natural.
  • Postings about the “Attack of the Mole People” either online, on polls, in Street Roots (alternative paper made by houseless population).
  • One of the investigator’s connections gets attacked.
  • Corpse of a mutated frog-monster is discovered.
  • The party gets contracted to investigate by the Authority faction (a dangerous option that entangles the investigators with this faction).

Potential Clues

  • Medical professionals have been sending victims of attacks with no insurance to Dr. Shelly’s clinic.
  • Dr. Shelly is being consulted about a deformed corpse.
  • Sewer grime on victims & frog-monsters.
  • Frog-monsters have a distinct smell of medical antiseptic underneath the sewer stink.
  • B&H delivery van spotted at various scenes of attacks.
  • A pattern in the location of attacks surrounds an abandoned sewer expansion project.
  • Small flier for a medical study put on by Dr. Shelly is either on a frog-monster or in a missing person’s home.
  • Video cameras catch glimpses of frog-monsters.

Frog Monsters

  • New frog-monsters are feral hunters drawn to infect others.
  • The longer they survive the more intelligent some become.
  • Inherent within them is a drive to worship the Old Powers, which leads their violence toward becoming more ritualistic and arcane in nature.

Infection: If an investigator suffers critical damage from a Frog-monster’s tongue, they become infected.

  • Infection can only be stopped through cutting edge science or magical means.
  • The victim slowly transforms (increase Str & Dex by D6).
  • After the change they need to succeed in a daily CTRL save or be lost to the party

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Name: Dr. Shelly

8 HP 10 STR, 10 DEX, 14 CTRL

Syringe (Dex save or incapacitate),

Gun (D6), reading Tome (D6 Stress)

  • Face-cast: Tilda Swinton the scientist consumed by the occult.
  • To continue her research, to complete her part, to ascend.
  • There is no line she won’t cross in order to bring about the Plague of Frogs.


Name: Mr. Sims

13 HP, 1 Armor, 14 STR, 14 DEX, 14 CTRL

  • Impeccable gray suit, trailed by a non-euclidian shadow.
  • Face-Cast: a much older Mads Mikkelsen.
  • To collect, to corrupt, to unlock.
  • Can heal using drones as fuel (drones). Can make more drones.
  • Delegated Magic: Can cast chaos magics through conduits, consuming their souls and sundering their flesh.


3 HP, 10 STR, 10 DEX, 10 CTRL

Hands or tools (d6)

  • Currently there are two drones in active use.
  • Coveralls with B&H embroidered on the front, a large white van with B&H Delivery.
  • Glassy look to them. Sometimes their color ain’t right (skin, hair, clothes, everything).
  • To follow. To be used.
  • Can ignore the first instance of critical damage. Does not retreat unless it’s master wills it.

Frog Monster

Stats range from:

4-8 HP, 0-2 Armor,

13-16 STR, 12 DEX, 10 CTRL

Claws (D6) Tongue (D8)

  • Humanoid frogs. Large, muscular. Some are able to hide their form

  • To remain hidden. To free their master. To inherit the earth.

  • Critical Damage: Victim becomes infected Frog-Monsters

Frog Priest

8 HP, 2 Armor, 13 STR, 12 DEX, 15 CTRL

Tongue (D8), Void Touch (D6 Stress)

  • Runes carved into its flesh (like those upon the altar it created).
  • To complete the Ritual of Incursion, to uplift the frog-monsters, to lead.
  • It is able to carve permanent marks into it’s victim’s using it’s Void Touch.
  • Critical Stress: It’s own rune’s start to bleed purple flames causing 4 stress to all in the vicinity.

Potential NPCs to Prep

  • Social Worker
  • Police Officer
  • Bartender
  • Sanitation
  • Mortician or Heath-care provider
  • Member of the houseless community

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Dr. Shelly’s Clinic


  • From the outside Dr. Shelly’s clinic is extremely nondescript.

Main Level

  • The inside is sparse.
  • Eggshell white waiting room with mint green vinyl chairs and an empty reception desk.
  • The back areas look to be surprisingly underused for how many people are listed on the sign in logs (many of the names seem fake).
  • Large supply closet is empty except for a shelf (hidden stairway to below).
  • There are cameras everywhere.

Hidden Lower Lab

The lower lab level revolves around the large Sterile Operating Theater[A] with an attached space leading away from it in each direction (B-E going clockwise).

Sterile Operating Theater [A]

  • Partially dissected person/frog.
  • Large tubes with different stages of frog-monster floating in viscous liquid.
  • Multiple tables with heavy duty restraints.
  • Extensive drills,saws, knives, syringes.

Staircase [B]

  • To the north of the operating theater.
  • The only way to get to the clinic from the lower lab.

Office/Living Area [C]

  • To the east of the operating theater.
  • A large converted office area.
  • Every inch of the room is covered in diagrams, photos, scientific notes interspersed with ancient languages and occult iconography.
  • A small desk has a single old leather book upon it (Ogdoad’s Well).
  • Tucked in the back of the tome is a receipt from B&H delivery.
  • Behind two movable whiteboards is a small cot and hot plate.
  • There is a CCTV monitor and door control system in this room.


An ancient tome written in an unknown language. Multiple diagrams within the book of a race of primordial humanoid frogs. Anything more than flipping through the book causes D4 stress.

Holding Pen/Sewer Exit [D]

  • To the south of the operating theater.
  • A wide hallway with reinforced doors at either end
  • Plexiglass holding pens line both sides of the hallway.
  • One pen has 0-3 Frog-Monsters
  • The other pen has 0-2 drugged humans
  • The farthest door opens on to the sewer.
  • All doors in this area can be controlled remotely from the office.

Walk-In [E]

  • To the west of the operating theater.
  • A freezer with multiple bodies stored within.
  • A rack filled with tagged samples on the back wall.
  • On the middle shelf are seven large vials of neon green liquid (labeled in an unknown language).

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The Sewers

Exterior Entrance

The main entrance to the sewers is an abandoned work site that has been fenced off and boarded up.

  • Close inspection shows that (the fence has a large hole in it.
  • The boards have been removed.
  • There is evidence of heavy traffic in and out.

Interior Sewers

The sewers are dark, wet, and at times cramped.

  • As the investigators explore the tunnels the more they become filled with a thick, sticky membrane (like from the chamber in Aliens).
  • Use sound/shadow to indicate being followed, but actually they’re being led).

Things That Can Go Wrong Deep Below Ground

  1. Equipment lost or broken.
  2. Investigators get separated.
  3. Getting ambushed by a Frog-Monster.
  4. Caught in sticky membrane
  5. Getting lost/lose the path back.
  6. Hear the cries of a person in distress deeper in the sewers.

Crossroad Within the Deep

Eventually the investigators should reach a crossroads down deep within the sewer system. To the left is Dr. Shelly’s hidden lab (Holding Pen/Sewer Exit [D]) , and to the right leading deeper toward the Frog-Priests altar.

Provide Clues to what would be down either path.

  • Lab: A medical antiseptic scent, the drone of generators, fluorescent lights.
  • Altar: The flicker of flame, chant like droning, strange markings upon the wall, increased instances of membrane.

After a choice is made: This crossroads is a perfect place for the Frog-Monsters to set up a trap for when the party is trying to escape.

The Frog Priest’s Altar

Off of a main sewer line is a side passage that curves into a chamber.

  • The space is filled with candles that illuminate the sigils painted along every inch of the wall
  • Opposite the entrance is a large altar made from multiple frog bodies splayed open in impossible angles.
  • Close inspection reveals that all the bodies making up the altar are still “alive.”
  • Kneeling before the altar is the Frog-Priest, often attended by two small Frog-Monsters, half the size of those they’ve seen before.
  • Investigators witnessing things in this space will receive stress. Most likely it would range from: Contact (D4 Stress) to Exposure (D6 Stress).

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Liminal Horror was written and designed by Goblin Archives