More Monster Metrics, Pt. 2

As mentioned last time, here are the results from v1.08 of the Monster-Metrics function of the Arena simulator. This shows how each monster from the OD&D dungeon tables match up with generic Fighters of levels 0 to 12. Equiv. HD (EHD) is what I would use to award XP now (using the original rule of 100 XP per HD). Or, for greater simplicity, you could look at the number of asterisks in the "Bonus" column and give that number of extra increments to XP (hat tip to the Cook/Moldvay notation).

Shading of the monster names indicates broadly where monsters were in the original six Monster Level Tables (OD&D Vol-3, p. 10-11). Although, if we were to revise those tables based on this data, it suggests that we could do something like this -- Level 1 would be all monsters shown with EHD 1; Level 2 would be EHD 2; Level 3 EHD 3-4; Level 4 EHD 5-6; Level 5 EHD 8-10; and Level 6 EHD 12+.

Thanks to the capacity for Party-on-Party combats in the current simulator, we can now gauge not just balance against one Fighter of similar level, but exactly what it would take to balance a given Monster against fighters of any level. (Recall: All fighter are assumed with 3d6 stats, chain and shield, +1 sword, no other special abilities). Where a fraction appears, it means that it takes several of the monsters to match a given fighter; e.g., in the top right, the "1/16" means that it takes about 16 Giant Rats to take on a solitary Lord of 12th level. Or where an integer appears, the reverse is true: the "17" in the bottom left, indicates that a Vampire is a fair match against 17 normal men-at-arms, under this model.

I think that the most important observation here is that not all monsters scale the same when you put them in groups, or face them off against higher or lower-level PCs. Two distinct categories of special abilities present themselves:

• Low-Level Killers: These are area-effect attacks, which can affect possibly an entire party at the start of a combat, but are limited in terms of times used (e.g., Breath Weapons) or being easily countered (e.g., avert eyes from Gaze Attacks). These abilities are likely to destroy large numbers of low-level fighters, but are of more limited use against higher-level PCs (who are likely to make the save and then keep fighting afterward). This is passingly similar to the magic-user "glass cannon" effect; a nuclear-type option that you can shoot off only once or twice. 


• High-Level Killers: These are predominantly save-or-die-on-hit effects, that can only affect one target per round, but can be used round-after-round without limitation (e.g., Poison, Petrifying Touch, or Swallowing). These are unlikely to have any benefit whatsoever against low-level fighters; the target is likely to be dead anyway just from the 1d6 damage attack. But this effect is far more worrisome for high-level characters; if a Lord falls into a pit full of poisonous Spiders, the small amount of direct damage is of almost no concern, but the possibly multiple save-or-die rolls each round is a real problem (and the Lord's high hit points then become effectively irrelevant).

Granted that monsters scale differently in groups, I still wanted to generate a single value that we could use for experience awards (EHD), which incorporated all of the information across different levels of opponents (a more stable, consistent measure than before). So the metric I decided to use was to multiply the number in each cell times the level in question (that is: total raw hit dice value at that level), and then take the average of that across all levels 1-12. That is: \(EHD = (\sum_{n = 1}^N n \cdot f(n))/N\), where \(f(n)\) is the monster metric at level \(n\) in the table above, and \(N\) is the maximum level considered (in this case, \(N = 12\)). I think that overall this gives pretty good EHD figures.

Using these more robust EHD values, we see that some monsters have increased in value from our prior point estimates. For example: Spiders and Ghouls previously didn't seem to warrant any bonus to XP for their abilities; and we can see above that indeed, their special abilities do not put them at an advantage over a single 1st-level Fighter. But when appearing in groups their save-or-go-down abilities are much more dangerous; according to our data, it only takes 3 Ghouls, or 6 Spiders to threaten a solo 12th-level Lord with likely death in combat. Overall, then, we can confirm that they do warrant an XP boost across all the situations where they might appear.


Anything surprising you can see in that output data? Next time we'll focus specifically about the monsters with the uppermost EHD values in that table.