I’m currently umm-ing and ahh-ing as to how to approach monster conversion.
I’ve got a homebrew game system based off White Box OD&D, and am running an open table Barrowmaze campaign using monsters from Labyrinth Lord (which is the module’s system of choice) and Old School Essentials - thus there is some conversion required to bring stat elements in line with a d6-heavy game. That’s pretty straightforward. d8 becomes a d6+1, d10 a d6+2, etc.
Armour reduces damage rather than increasing difficulty to hit (single-roll combat), however, so I need to do some quick mental calculations to convert on the fly (every 2 points of difference from an unarmoured human is roughly 1 point of damage reduction).
Saves aren’t too bad, though ‘Save as Fighter’ tends to require keeping an extra reference table close by.
But I am flicking through games like Black Hack and Swords & Six-Siders which largely base all of a monster’s figures off its HD value (HD affects damage output, comparing PC and NPC HD to determine a roll’s difficulty, etc).
Is that too lightweight to be helpful to other systems?
If you were in the middle of a game and looking to convert a monster from this OSR module the group is running through (and, indeed, from the vast library of setting material out there in other game systems), what is the minimum information you need to work out a monster on the fly?