The Design Mechanism produces and publishes the Mythras roleplaying game, the acclaimed and innovative percentile system. Mythras is supported by an extensive range of supplements and adventures, featuring everything from Sword & Sorcery to Science Fiction and Urban Fantasy Horror.
Stop Press!

Between now and the end of January 2023, we're offering the Classic Fantasy supplement in PDF for Mythras and Mythras Imperative at the amazing price of just $0.99. 

For less than a dollar you can access the whole rules-set designed to bring the Old School dungeoneering experience to d100 roleplaying, complete with classes, character ranks, monsters, treasure, and everything else needed to scratch that dungeon delving itch.

Classic Fantasy includes:

  • 11 Character Classes
  • 7 Character races
  • Full rules for Passions as Alignments
  • Battle-Board combat
  • Arcane and Divine spells for Ranks 1 to 3
  • 40+ monsters
  • 100+ magic items
  • Deities and Cults

Watch out also for Classic Fantasy Imperative - a free introductory rulebook that will be launched under an open license and accompanied by its own SRD.

Mythras Core Rules

This is the full rulebook, containing everything you need for fantasy adventures.

  • Character Creation
  • Equipment
  • Skills
  • Combat
  • Magic
  • Cults & Brotherhoods
  • Creatures
The latest errata and updates for Mythras can be downloaded here.

Mythras Imperative

A free introduction to the Mythras system, and geared towards generic adventures. Mythras Imperative contains basic character creation and combat, introduces the core concepts of the game and gets you adventuring straight away. The ideal gateway to Mythras. 

Just click on the cover to download your free copy!
Mythras Character Creation Workbook

A free tool to aid players when creating Mythras characters. Contains the character sheet, summary charts of attributes and skills by culture and career, and a handy skill allocation sheet to assist in allocating skill points at each stage in the process.
Mythras Firearms

A free supplement, Mythras Firearms brings rules for all kinds of firearms to the Mythras game system: muskets and bolt action rifles, through to modern machine weapons, and even weapons for Science Fiction settings, such as lasers and blasters. Introducing new combat options and Special Effects, it takes a sober and realistic view of how firearms impact roleplaying games, while being easy and fun to add to the existing rules.

A print copy of Mythras Firearms is available from our Lulu Store.