Back to the Dungeon Role Playing Game OSR Universal D20 System

Publisher's blurb:

SO WHAT IS THIS? Tired of looking in the rulebooks and charts for how to do things with your OSR Games with ununified mechanics? Look no further for a unified SIMPLE OSR 0E BX D20 system is here!

MOST BASIC RULE! TO DO ANYTHING Roll a D20 and try to roll HIGH!

IF an Attribute Bonus applies then ADD or SUBTRACT it. Most Monsters and unimportant NPCs don’t have attributes but will have bonuses listed in their descriptions OR you can just simply make them up as the GM.

IF it’s something that you're SKILLED at then ADD HALF your Level or Hit Die if a Monster or NPC.