rpgs mothership horror sci-fi


Note: This document is a work in progress. As I make changes to the game, they’ll be reflected here (literally every time I save!). There will be disorganized and scattered notes and half-finished thoughts. If you’re looking for the most recent complete draft, you can find that here. Also, if you want to read more about Mothership, you can find all my blog posts about it here.

Character Creation

Roll [6d10] for your Strength, Speed, Intelligence, and Combat.

Pick a Class

You start with 0 Stress, 1 Resolve, and [Strength x2] Health.


Mothership uses standard d10s for all of its rolls, though it uses them in 3 different ways. The most common way is to roll a percentile [0-99] on 2d10 [notated d%], using one die as the ten’s digit and the other as the one’s digit [we call this a check”]. The second way is to just roll any number of d10s [notated xd10] and add them up [2d10 can generate a number between 2-20]. The final way is to roll a number of d10s and add them up as multiples of ten [2d10 can generate a number between 20-200] we notate these rolls as xd10. That’s a d10 underlined).

How to Play

Whenever a PC wants to do something and the price for failure is high, then they must roll under the appropriate ability on d%, otherwise they fail. A roll of double (the same number on the d10 and the d10) indicates a critical. If the roll was a success, it’s now a critical success. If it was a failure, it’s now a critical failure. A roll of [00] is always a critical success and a roll of [99] is always a critical failure.

If the PC has a situational advantage (for instance, if they have a skill that would be relevant), then make a d% roll as normal, but instead of rolling 1d10, roll 2d10 and take the best of the two dice, before adding the final 1d10 to the result.

If the PC has a situation disadvantage (like working in the dark without a light, or trying to do something while under attack), then you roll as above, except you take the worst of the 2d10 before adding the final 1d10 to the result.

Contested Rolls

When two parties directly compete (grappling, surprise, chasing, etc.) they both roll as usual and whoever rolls higher, without going over their own stat is the winner. Critical successes beat regular successes even if they rolled lower. Tied successes require a re-roll.


To determine who goes first, each side makes a contested Speed check, the winner chooses whether to go first or last. When testing for surprise, make a contested Speed vs. Reason check. If you successfully surprise another character, you get an extra round before they do, and can choose whether you act first or second for the remainder of the combat. Fighting is resolved by a contested roll with the attacker making a Combat check against the defender’s Armor save. If the attacker succeeds, they roll damage dice equal to the d10 rolled.

It’s not necessary for most opponents, but if it becomes important, the d10 rolled on your combat check can determine a hit’s location: [1-2: legs, 3-4: arms, 5-9: torso, 10: head]. Even” rolls mean the left side was hit, while odd” rolls mean the right side was hit.


Human NPCs start with [1d10x10] Health. Aliens start with [1d10 x5].


Every PC has four Saves which are used to determine whether a PC can withstand or resist a different type of effect. Armor Saves are used in combat and have already been explained. Reason Saves should be used whenever a PC is confronted with something that defies logic or bends the laws of reality. Psyche Saves should be used for fear or loneliness. Body Saves should be used for hunger, disease, or anything else that might invade or grow inside a body.

To make these saves, a PC just needs to roll d% under their Save. Failure usually means damage either to a PCs health or a Panic Roll.

Additionally, whenever you fail a Save (other than Armor), you can increase your failed save by 2% permanently.

Stress, Panic, and Resolve

Whenever a PC fails a Reason, Psyche, or Body save, then they must make a panic roll. Roll 1d10 and add any Stress the PC has incurred to the roll and consult the table on the back of the rulebook. PCs may ignore a number of stress equal to their Resolve. Stress is gained primarily through Panic rolls.

  1. Focus: Gain advantage on all rolls for the next 1d10 minutes.
  2. Anxious: Gain 1 stress.
  3. Nervous: Gain 2 stress.
  4. Cowardly: 1 stress. Mental save or flee all combat.
  5. Hallucinate: Lasts for 2d10 minutes.
  6. Afraid: Gain a new phobia. Reduce 1 stress.
  7. Broken: Disadvantage on all rolls for 2d20 minutes.
  8. Paranoid: Whenever a PC or NPC joins your group (even if they only left for a short period of time), you must make a Psyche save.
  9. Deathwish: Attack or head towards the closest enemy for xd10 minutes (x=stress).
  10. Unconscious: Fall unconscious for xd10 minutes (x=stress).
  11. Broken: Roll on the panic table whenever a friendly nearby PC fails a save.
  12. Psychotic: Attack the closest PC ally until you do 2d10 damage (Secretly rolled by the GM), or are knocked unconscious.
  13. Lights fading: Roll twice on this table. Insanity in 1d10 minutes without intervention.
  14. Insanity: You become an NPC.

PCs can reduce their stress by 1 for every night of uninterrupted sleep, or for going a day without having to make any kind of Save. However, time spent in cryosleep or hibernation does not reduce stress.

Leveling Up

PCs can level up after they have survived a number of sessions equal to their current level (1st level characters level up after one session, 2nd level after two, and so on…). Every time you level up you may choose one option

Note: everything below is total work in progress notes and scraps type stuff.


Outer Space travel

As opposed to coming up with specific travel times, I think based on the type of ship we can outline some basic timeframes which can then be randomize with a d10 roll. D10 weeks, d10 years, etc. and then once those distances are established, you can go from there.

Ship Interplanetary Interstellar Intergalactic
Cruiser Weeks Years Millennia
Miner Days Months Decades
Colony Hours Weeks Years

More Panic stuff: Screaming, drawing attention that sort of thing


Point buy system since money seems irrelevant in space. Maybe rolls on different tables. Weapons for marines. Equipment for scientists. Teamsters get a roll on each. Androids get to pick one thing maybe. Or no equipment at all. Or they have their own table of equipment like mods” that give them certain abilities.

There’s also probably a standard list of equipment that come with a ship: space suits, basic assortment of tools, weapons on a military ship, that kind of thing.

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