You want to run an adventure statted for 3.x, or borrow some favorite monster for it. How do you get that over to Old School Hack? Here are some guidelines to be helpful—feel free to adjust the end product. This is to get you inspired, give you some tools, and get you started.
Armor Class. Ignore Dex bonuses and shields. Subtract 5 from the remaining total.
Wounds.Grant 1 wound per Hit Die up to 3, then +1/2 for 4 Hit Die and up. For less formidable high hit die monsters, just keep the hit die.
- 1-1, 2- 2, 3-3. 4-6, 5-8, 6-9, 7-11, 8-12, 9-14, 10-15, etc.)
Damage.Lousy fighters get no weapon type. Competent fighters get a type: light, heavy, reach, very heavy, ranged.
- For every full 5 automatic hit points of damage, assign 1 additional wound for each attack.
- Creatures with multiple limbs can get multiple weapon advantages at once; an otyugh with tentacles and a maw can get the +1 AC for a reach weapon while biting as a heavy weapon if desired, for example.
(The rest is advice on a “competency bonus” and how to handle talents and saving throws. It’s in a .pdf because formatting nested points online is… not optimal. You all would rather have me spend time designing cool toys than wrassling stupid format hassles, right?)