One-Page System Rosetta

Being all one really needs to play with the SDM rpg system.
As originally presented in the UVG 2E.

The Traveler is a PC in the best tradition of roleplaying.


When PCs try something risky, they roll d20 + ability + skill and try to beat a target number.

  • 3: trivial. Only relevant for critical failures (natural 1).
  • 7: easy.
  • 11: mediocre.
  • 15: hard.
  • 19: very hard.

Advantage & Disadvantage

The referee assigns a relevant bonus [+] or penalty [-] when circum- stances favor or hinder a character.

  • +1/-1: a tiny advantage or disadvantage.
  • +6/-6: a rather large advantage or disadvantage.
  • +1d6/-1d6: a pretty random advantage or disadvantage.
  • roll two dice … and take the better or worse. Also possible.


An abstract measure of power. PCs start at level 1 and go to level 9.


The narrative resilience of a character. Exactly like hp, but fuzzier. When life hits 0, a character is in deep trouble.

Six Abilities

Range from 0 to 5, like modifiers in 3d6-style games. A 1st level PC assigns 7 points to their six abilities.

  • Strength: lifting bars, bending gates.
  • Endurance: pain, strain, and long-distance running, ha.
  • Agility: precision, speed, and dodging.
  • Charisma: force of personality, luck, divine favor, ba.
  • Aura: psychic fortitude, power of soul, ka.
  • Thought: intellect, education, and praise ibis-headed Thoth.


What one is good at. Applies when it makes sense. Can be a job (historian, bricklayer, priest), something narrower (sleight of hand, melee combat), or something weird (project management, golem whispering). A 0 level character has two skills.

  • Skilled: +3 bonus to rolls.
  • Expert: +6 bonus to rolls.
  • Master: +9 bonus to rolls.


When nothing but blind luck might apply.

Roll d20 + Ability over 13 to avoid doom (or a nasty rash).


When a PC does not want to get hit. Like ascending AC.

10 + Agility + Armor


A cinematically suitable amount of time to take an action.


Roll initiative every round for each side. A random PC rolls for the group every round. The side that rolls high, goes first. If there is a tie, chaos reigns and everything happens at once.

d6 + Agility


Usually, a character moves and does a thing. Common sense applies.


When a PC wants to hit an opponent.

  • Melee: d20 + Strength + Skill
  • Ranged: d20 + Agility + Skill
  • Oldtech / Psychemagic: d20 + Thought / Charisma + Skill


Reduces a target’s life. At 0 life it becomes an ex-target. Most sentient targets do not want to be ex-targets and flee earlier.

dXX (weapon) + Ability (if applicable) + Skill (if applicable)


For every trait or item beyond their limit, a PC suffers -1 to all rolls.

  • Items (stones and stone-sized objects)7 + Strength
  • Traits (skills, mutations, innate powers)7 + Thought

Curses, disease, and other afflictions also occupy inventory slots.

Magitech and Fantascience

Life fuels spells. Bodies (ha), spirits (ka), and memories (ba) are consumed by the alien fires of magic. All spells are of the first power, unless otherwise noted.

1 power costs 1 life

Powers from d20 traditions with levels translate as follows:

cantrip = 1 power
level 1 = 2 power
level 2 = 4 power
level 3 = 6 power

So Pyreball (3rd level spell) costs 6 life.

Powers Enumerated

Hero Dice

d6s for modifying rolls and regaining life. Each PC gains 1 per session and every couple of hours. Can store HD equal to their level.


  • carousing: waste €1d6 x 100 (or more) to gain that amount of xp. Roll charisma on carousing table (e.g. p16) for side effects.
  • exploring: 1d6 x 10 xp for braving danger to see something new.
  • quests: 1d6 x 100 xp per session of progress towards goal.
  • referee’s discretion: as is tradition.

Levelling Up

Every level, a PC gains one of the following:

  • a new skill or improves an existing skill
    (skilled -> expert -> master)
  • a new innate power or mutation
  • increases an ability score by 1

“These rules are not enough!” cries the Goodling.

“Then peruse the 16-page form expressed in the Eternal Return Key,” replies the Blue Skull.