I was recently asked why I don’t include “Challenge Ratings” (CRs) for monsters in my old school Microlite games as that would allow people who want to design set piece encounters for their games to do so much more easily.
The answer is actually fairly simple. I neither have the time nor the interest to do so. Coming up with actually useful CRs for organically designed monsters requires lots of time-consuming testing — a lot of combats played out and carefully recorded to see just how difficult a challenge each monster actually presents and how much this varies with how the monsters is used in combat. As I have no personal interest in set-piece encounters and find combat to be one of the least interesting parts of the game (exploration and roleplaying are far more interesting to me), I really can’t see myself doing all this combat playtesting to come up with accurate CRs for 100+ monsters for those who would like to have them.
The only way to avoid all this testing is to what 4e seems to have finally done: decide what each CR means in terms of hit points, attack bonus, saving throws, damage per round, etc. and then decide what challenge rating a monster should be and use those stats. Unfortunately, it is impossible to design monsters organically that way. You can’t have a monster with the hit points of a CR 5 monster, an attack bonus that falls between CR 1 and CR 2, the AC of a CR 7 monsters even if that’s what would accurately describe the monster. And this is before you have to consider special abilities which by their very nature are hard to quantify accurately in a CR system. I have zero interest in monsters designed to fit a CR formula instead of designed organically to fit their niche in a setting. Besides, monsters from the old school games my Microlite20-based systems emulate were not designed according to a formula so changing them all to be designed around a formula would “break” them both from the point-of-view of player expectations and using old school modules with the game.
What this basically boils down to is that while my Microlite7X and Microlite81 games certainly can be used to play out carefully-balanced set piece encounters, they are not designed for this style of play and do not provide any easy way to design such encounters. If you want to use my games this way and need an accurate CR-type system, you are going to have to design your own as I am unable to provide such a system. For a very rough system, you can take the number of hit dice of a monster has and add +1 for each special ability (if any) and -1 for each special weakness (if any) and consider that the monster’s Challenge Rating. Yes, I know that is probably not nearly accurate enough, but it is the best I can provide.