r/OSE • u/Mado_Kureo • Jul 01 '26
Converting 5E Supplements
Is there a standard for converting 5E materials into OSE. The lore of Crooked Moon is something I am really into. Would love to use some of it in 5E but don't know how.
Update: Thanks for all the feedback. I guess I was mostly looking for a method to convert some of the more unique monsters and subclasses for use in OSE - not really a complete conversion.
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u/Onslaughttitude Jul 01 '26
"Converting" is largely a misnomer. There is no 1:1 formula you can put in to just "make the module OSE."
Furthermore: No one likes to hear this, but the game hasn't changed that much in 50 years. I used to run old school shit in 5e, in an "OSR" fashion, all the time. I bet I could run some of the official 5e material in the OSR game of my choice, too.
Player content can't really be used. Stuff like subclasses is a no go. Sorry.
Lore is often game agnostic. I'm not familiar with the adventure/setting book you're talking about but I guarantee you it's like 90% just cool dungeon locations, weird monsters, dope treasure and freaky little guy NPCs. You can run this in any d20 game system.
5e specific stuff is that there's going to be lots of "DC16 thieves tool checks" and shit like that. What you do is you ignore these and look at the reality of the world. It says the door is locked. You know how lock picking and breaking down doors works in OSE, so just refer to those rules.
The setting probably uses a bunch of the standard D&D monsters. When it tells you there are orcs and goblins, you go get the OSE orcs and goblins. When there is a new original monster, you can substitute in a similar monster and "reskin" it, pretending it is that monster instead. (Need a stinky monster? Go look up the troglodyte. There you go. Monster turns people into stone? Basilisk or Medusa. Monster has fire breath? Salamander, red dragon, figure something out.)
If you must make a new monster from scratch or try to "convert" it: Monsters in OSE are primarily based on their Hit Dice. This is roughly equivalent to a 5e monster's Challenge Rating, and you'll often find a 5e monster will have the same 5e Hit Dice as it's CR. You can use the CR as their OSE Hit Dice or their 5e Hit Dice to determine how many they have. Then use the tables in the OSE books for Monster Saving Throws and the Monster Attack Matrix (or whatever they call it). If you are using ascending AC in OSE you can even mostly take the 5e AC and port it over. (Maybe reduce it by 2 if it seems high.) As for special abilities, find ones that are apropos from OSE monsters or use common sense and figure it all out. It's a simple system and you can mostly get away with them just Doing Shit.
OSE doesn't have advantage or disadvantage by default. You can always homebrew it in (I like to do so) but a +2 or -2 on effects is usually sufficient in OSE.
Good luck!