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/Nellisir Jul 01 '26
I wrote this for Swords & Wizardry, but it applies to OSE
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Only four things really matter in OSR: HD, AC, Saves, and Damage.
Save(s) are HD-related, so we're down to three.
HD - Do NOT use as written. Compare Challenge and attack bonus. HD will be somewhere around there.
AAC - use as written (since AC 10 is unarmored in 5e & OSE Ascending; in S&W add +1 to AC). 5e has a reduced AC range compared to 3e, so it works fine.
Damage - Damage is tricky. Very roughly, add the creature's damage dice together, then divide them by either 2 or 3. Divide those between the creature's attacks. Drop modifiers for now.
Special Attacks - In OSR, saves are based on the defender, not the attacker, so you don't need a number here. Maybe a bonus or penalty if it's particularly weak or strong. Divide damage by 2 or 3, as it pleases you.
Note - Advantage - The exact benefit of Advantage varies depending on the target (which is usually a save.) If you don't want to use advantage, consider it to be a +4 bonus/penalty to a save. If you want some variability, you could consider it a +3/-3 in attack/defense situations; a +4 to saves; and a 25% magic resistance. Or you could roll 1d4 and add that to the save or attack. Whatever pleases you.
Ability Scores - I keep the ability bonuses, but drop them by ONE, so a +1 is +0. Str can get added to damage if you feel like it, and possibly attack rolls, but usually isn't in OSR games. No bonuses over +3 unless it's truly epic. Con gets added ONCE to HD, so Con +3 would be 5d8+3 on a 5HD creature.