I'm working on an OSR mashup of games, but my old-school experience goes back only as far as AD&D 2e. I'm using a modified THAC0, theatre-of-mind (no grid), classes and races, memorized spells, a thieving table, maybe roll-under skills...(don't worry - it's just for fun)
What am I missing? What makes a game OSR to you (that isn't the actual book by TSR)?
The central feature of the OSR is compatibility with TSR D&D. Barring that, the most important peripheral features IMO aren't the same ones typically quoted from the primers and the principiæ.
• In an old-school game, the DM must abandon the idea of precious plots, or the notion that it's a waste of time to create content that the players never encounter. The DM is building a sandbox world: the players may never see whole swaths of it. So the game rules have to make world-building and dungeon-building
easy. Tables for procedurally generating hexes and dungeon rooms and monster encounters and treasure hoards are appreciated. All the better if they're structured in such a way that they generally match low-level monsters up with low-level treasures, upper dungeon floors, and more populated hexagons; vs. high-level monsters with high-level treasures, deep dungeon levels, and wild wilderness. Also, something that most OSR games don't bother with (beyond the odd dungeon-restocking table) but should: rules for evolving the game-world dynamically, including dungeon restocking, overworld events, and alterations to wilderness hexes over time.
• In an old-school game, the players must abandon the idea of precious protagonists. Not just because characters can die, but also because characters will take time to do things that remove them from ordinary play (like healing up from wounds, doing research, crafting or building things), while time in the campaign marches on. And so you can't always take your favorite or highest-level or best-equipped character on every adventure. Sometimes your favorite fighter is healing up for a couple of weeks, and so you need to take your lower-level magic-user, or your hobbit who only carries a +1 sword, for a spin. So the game should support fast, easy, partly random character generation without too many decision points—no need for "builds," in other words. Characters get more powerful mainly through what they do and find in the game world (fighters find cool magical arms, mages collect cool items and spells), and this should broadly outweigh characters getting more powerful through level advancement alone (like clerical spells or thief skills: better for a thief to find
elven boots than run up his Move Silently percentage).
• In an old-school game, we generally want to model or simulate reality without relying on tedious rules to do it. That is, the referee is there to make rulings so that the game-world operates according to common sense and logic, and nobody has to look anything up on huge tables or do physics equations or consult a textbook on economics. The DM just applies their best judgement. For some things, like combat, they're important enough to have detailed rules, but still abstract because it would be an utter pain to model real wounds and weapon strikes—so we offload that onto a simple system like HP, AC, and attack rolls. But where it counts—planning expeditions, carrying supplies, counting rations and torches and arrows, hiring henchmen and porters and grooms and bringing along animals and carts and so forth—while some OSR games try to abstract this sort of thing away too, it's probably not the best idea to handwave such a central feature of a game that's ostensibly
about exploration. So you want your game instead to include mechanics that make things like encumbrance and resource-tracking and henchman-wrangling as effortless (and even
fun) as possible.
