Spooky action at a distance

Derelictcrawl Procedure for Mothership

A turn based system for your sessions that increases risk and elevates the Warden’s tasks. I’ve been using a version of this for a while to help me keep track of when to give out Stress, when to roll for Panic, encounters etc. I like how the overloaded encounter die just tells me what happens and lets me focus on narration. So after a bit of refinement, I present you this little procedure.

I strongly recommend using the encumbrance house rule by quadra (you’ll have to scroll down a bit) to make the risk/reward of losing supplies and pushing further into the derelict meaningful.

The Exploration Turn

When exploring a derelict (or any location containing rooms) time is divided into turns. During an exploration turn, the crew may perform one significant action: moving between rooms, searching or exploring a room, attempting to force an airlock open, and so on. The derelict die is a special kind of die that is rolled every exploration turn.

After the crew declares their action for the turn, roll a d20:

Roll Effect Description
1 Panic The crew makes a Panic Check.
2-4 Encounter Warden rolls on the encounter table. If there is only one monster in this location, encounter it instead. Note that not all encounters start as violent.
5-7 Horror The crew discovers something frightening and each character gains 1 Stress.
8-10 Setback Equipment breaks, supplies diminish. Choose what is most relevant for the moment. If the crew is using oxygen tanks or batteries, they are depleted by 1 hour. Bioscanner software starts glitching etc. Positive temporary effects end.
11-13 Locality The environment changes around the crew. An airlock closes behind, alarms go off, machinery activates or stops.
14-16 Clue Hint, warning or omen of an encounter. Ooze coming out of a locker, bullet holes in the wall. Think of the aftermath of your monster’s abilities.
17-19 Free No additional effect this turn. Negative temporary effects (such as conditions or extreme weather) end.
20 Regroup The crew reaches a safe spot and can take a breather. Each character reduces Stress by d5-2, 1 being the lowest result.

You don’t have to follow the roll precisely if it doesn’t make sense (like a Regroup on turn 1). When that happens, use adjacent entries as the new result. Go one entry down the table (↓) for a more positive event, go one up (↑) for a more negative one.

If you want to even out the probabilities, you can use a d8 instead. I just wanted the Warden to also get their own special die (like the players have their panic die).

A Note on Doors and Scale

This section is inspired by exploration procedures in Errant.

The crew’s progression through a derelict will often be blocked by various barriers. Here are some examples of how you can adjudicate getting through them.

  • Airlocks take an exploration turn and a successful Strength check to force open.
  • Laser cutting a passage through metal takes 2 exploration turns.
  • Locked doors can also be bypassed via hacking. Successfully bypassing a lock does not take an exploration turn, but a failed attempt does.

(Terminology extrapolated from Gradient Descent.)

Usually it takes only one turn to fully explore a room. Still, the crew might encounter cargo or even industrial scale rooms which take longer to cover.

Scale Description Exploration
Human Made to contain humans. Offices, control rooms, crew quarters. 1 turn
Cargo Large storage areas and bays, still accessible to humans. 2 turns
Industrial Factory floors, sewers, starship cores. Aren’t designed for traversal. 3 turns

The crew can pick up their pace and reduce the number of turns needed to explore the area fully. However, they might attract unwanted attention. +1 human scale room per turn, or -1 turns to explore larger rooms. Roll next derelict die at disadvantage.


Turns represent an abstract amount of time it takes to perform an action. On average, they are equal to around 10 minutes of game time. And thus, 1 hour passes in 6 turns.

Some time-reliant items converted into turns:

  • Rebreather: 2 turns without resurfacing.
  • Oxygen: standard supply is 6 turns. For more unpredictable play: instead of tracking turns, deplete your O2 supply when you roll Setback on the derelict die. I imagine a character will get a warning light on their suit, leaving them one turn to replace their O2. Each resupply will last 6 turns on average.
  • Jetpack: enough fuel for 6 turns. Same method of tracking with Setback can be used as with the O2 supply.
  • Drones: can run for 12 turns.
  • Vaccsuit: can be fitted with an O2 tank with up to 72 turns of operation time, 24 turns if under stress. You can approach this narratively, or count >10 Stress as entering a stressed state.

And as always, feel free to to change things around. If you swap encounter and panic on the derelict die table, you will get a more physiological horror vibe from the session. Changing the amount of turns it takes to explore a room can make the location feel smaller or larger.

Further Reading

  1. Necropraxis - Overloading the encounter die: the original overloaded encounter die post.
  2. d66 Kobolds - The sci-fi encounter die: more sci-fi themed tables, including hex crawls and jumps.
  3. Save vs TPK - Houserules: a similar idea as mine of introducing a hazard/encounter die in mothership.
  4. Was it likely - The Peril System: an rpg that uses the encounter die as a core mechanic.
  5. Prismatic Wasteland - Exploding the encounter die: making the encounter die more reactive to player actions.

Published on February 6, 2022.

Tagged: mothership   osr   mindmeld   house rules  


Spooky action at a distance is a blog run by emmy verte, to muse on sci-fi, fantasy location exploration and short fiction. You can donate to support Ukraine here.