First, at the outset, we were hoping that we could reduce power levels to a single rating, together with, say, some formula for how many of the same type of monster interact. Our results show that this effectively impossible; interactions of complicated powers are, as we see again and again, fundamentally irreducible, and trying to use a simple formula or table will be essentially broken. For example: 3rd Edition D&D gave every monster a "Challenge Rating" and a simple formula: doubling the monsters increased this value by +2. But we are more keenly aware that some monsters have abilities that are lower-level-killers (area effects), and others high-level-killers (save-or-die on hit), and these interact totally differently against masses of low-level opponents, or small numbers of high-level opponents. If you want to use our ratings for encounter balancing, then you have to look at the individual cell in the master table for the level that you're considering (EHD alone is less dependable). A graph shows that some monsters are working in totally different probability distributions for mass combats: for example, Red Dragons have a power-curve regression, while Purple Worms have a logarithmic-curve regression, and those curves actually criss-cross each other (reverse advantage) as we advance in opponent level:
Second, in our master Monster Metrics table we summarized certain variable monster types the same way as they appear in the D&D encounter tables (e.g., Lycanthropes, Giants, and Hydras as single listings). These probably deserve their own detailed analysis, but there's not too much surprising here: Lycanthropes' ability to infect opponents doesn't make much difference within one melee. Giants are brutes whose EHD remains about equal to the HD throughout. Hydras with their multiple attacks and maximized hit points are always worth about double their base HD. Also shown below: Vampires with variants for summoned Wolves and Rats (but don't entirely trust that, subject to rulings discussed in the last article).
Third, of course, Dragons are the most complicated and possibly dangerous type in the entire ruleset. The master list only assessed Red Dragons, and represented an average across all age levels (randomly determined for each dragon encountered, a d6 roll indicating age level and points for each hit die). So they also deserve to be broken out for each type and age category, as below. We see that Young and Very Young dragons are worth about the same as their base HD. Sub-Adults are worth double value (a one-asterisk "bump' in XP). Adult dragons are worth triple value (two-asterisk bumps). Old and Very Old dragons can be worth anywhere from triple to sextuple value -- up to EHD 62 for the Very Old Gold Dragons, and that's not even accounting for any spell abilities!
Fourth, I went through the Moldvay/Cook rules to compare the "asterisks" they gave to each monster to the ones I've got here (the notational notion, of course, being taken from those luminaries). Where we differ, my results suggest that XP bonuses were somewhat overvalued in the B/X rules; this is compatible with the observation that while prior writers usually gave an XP "bump" for every significant special ability, not all work in synthesis for a monster at once.
- Same in B/X: Centipede, spider, berserker, ghoul, ant, beetle, giant, troll, scorpion, gorgon, medusa, purple worm.
- Higher in B/X: Lycanthrope, gargoyle, snake, mummy, cockatrice, spectre, hydra, wyvern, basilisk, chimera, dragons.
- Lower in B/X: Manticore, vampire.
Finally: If you want to run, double-check, or measure your own monsters with this same system, here's the program that will let you do that: MonsterMetrics is a Java executable JAR file, so it should run on any computing platform on which you have Java installed. Here's how to get it: (1) Download and unzip the first file below, MonsterMetrics.zip, to a location of your choosing (includes executable MonsterMetrics.jar and necessary data files). (2) Open a command-line prompt in that location and type: java -jar MonsterMetrics.jar. This will go through the entire included monster list and assess the strength at each level of opponent Fighter (running 200 mock combats per level/number combination in a binary search to find the best match), and also print a combined value for EHD at the end of each line (copy to a spreadsheet program for additional analysis). If you want to measure just a single monster, then append the name of that monster at the end of the line (for example: java -jar MonsterMetrics.jar vampire). Feel free to inspect the data file Monsters.csv and check out exactly how I adjudicated statistics for each monster in OD&D, and edit or add your own monsters to see how they stack up. (In addition, files for the source code and Java documentation are included for those who want to modify that, but as a standard user you can ignore those.)
Tell me how that works for you and your game!
- MonsterMetrics (Java ZIP package)
- MonsterMetrics Source Code (GPL license)
- MonsterMetrics Java Documentation
- MonsterMetrics Results Spreadsheet (ODS)