|Weight||HD||Attack 1||Attack 2||HP||To-hit|
Don’t assign an AC over 18, and don’t assign AC based on how tough the creature is: that’s what HP is for in creatures. So a monkey might be a one-hit kill but be really hard to hit because it’s so nimble, while a rhino only has an AC of 12 so you hit it almost every time, but boy that fucker can take the hits no problem.
For 99% of NPCs, they should just be 0-level fighters with 10’s across the board in terms of ability scores. Even like common soldiers are 0-level: it’s only exceptional people who have any levels in anything at all.
For particularly memorable NPCs, you might give them a +1 ability bonus somewhere. For super-duper awesome NPCs, you can give them up to +3 bonus points (so like an 18 INT, or 12s in CON, STR, and CHA, up to you). If you want to give more bonus points, you have to give some negatives as well. And feel free to give them abilities that “break” the rules, NPCs don’t have to work exactly that PCs, particularly if they have access to magic.
But what about magical creatures? The general rule of thumb with LotFP is that magical creatures are rare and dangerous. Any magical creature should be an adventure in itself, not just some mook in a dungeon. Like, a good monster isn’t a tactical mini-wargame, it’s a puzzle: and the prize for figuring out the puzzle is not having to play the tactical mini-wargame, because that unit in the tactical mini-wargame is wicked OP and unfair. And that puzzle can take an entire session and involve all sorts of crazy shit if done well.
So while the rulebooks don’t have a lot of guidance here, what does are the LotFP adventures. I’d recommend picking up Better Than Any Man—it’s free, and probably the second-best adventure I’ve ever read (after Vornheim). It’s huge, as this guy attests he got a dozen sessions out of it. I ran a 12+ hour marathon with it, and we only started getting into the shit towards the end. Just reading it will make you a better GM.
Then there are the OSR blogs. I read a bunch of these. My favorites are:
Check out False Machine and Monsters and Manuals, both have recently published adventures that are really great and have some awesome monsters in them.
Also, most the blogs are really good at tagging their posts, so find the like “monsters” or “encounters” or “rules” tag and follow the rabbit hole.
So in conclusion: (1) Dangerous is good. (2) Weird is better. (3) Follow things to their logical conclusions. (4) Don’t pull punches. (5) The rules are easy. (5a) Don’t mistake following the rules for playing the game.