L&E has some great rules on how to use ability scores for monsters, but sometimes you just don’t want to roll 3d6 six times in order for every monster the PCs capture and ask “so does this one have any exceptional traits”. (Because if your PCs are like mine, they will do that with every single monster.) So I have considered two different options for quick ability score generation, I’m not sure which one is better, but I thought I’d share both of them.
Option one: Roll 3d6 (once).
3: Three low scores
4-5: Two low scores
6-8: One low score
9-12: No exceptional scores
13-15: One high score
16-17: Two high scores
18: Three high scores
For each high or low score, roll 1d6 to see which score it is. If you roll the same score multiple times, add to the modifier. (For example, a roll of 17 on the table gets us two high scores. A roll of 1d6, twice, comes up Constitution twice, and so this monster has a +2 Constitution modifier.)
Option 2: Roll 3d6 (also once). If the result is less than 9, the monster has a number of low scores equal to your roll’s distance from 9. If above 12, it has a number of high scores equal to distance from 12. In either case, generate high and low scores as above (if a score already has a modifier of -3 or +3, and you roll it a fourth time, reroll. Unless you feel like just having something ridiculously exceptional, of course!)
The first option has the benefit of symmetry with rolling a single score, the second option is capable of generating monsters that have larger total modifiers (although it still gives us 45% of monsters with no modifiers, which is the same as option 1.)