Monte-Carlo Measures of Monster Levels, Pt. 5

See Part 1 for the table of Monte-Carlo measured Equivalent Hit Dice (EHD) for most of the monsters from OD&D.

Higher Level Special Abilities: Special abilities for monsters at the upper end of the table become a little hazy in how well the Arena simulator can measure them, because they're even more dependent on DM adjudication, initiative and movement, player knowledge about how to counter them, area-effects against multiple characters, etc. (As of this writing, Arena is only 1-on-1; but the next version under development will have party-on-party action, so stay tuned for that.)

Note that the Arena simulator doesn't model any tactical movement; the combatants are presumed to come to melee range and start alternating blows. However, for monsters that are characterized particularly by some special ranged attack, an "Entry Attack" phase was introduced, where we assume the monster in question gets exactly one (1) opportunity to engage in its special attack form before melee is joined. Thus: Giants hurl a single rock before melee, Manticores get one volley of tail spikes, Basilisks and Medusae get one gaze attack before melee (and so, each fighter must always save or be turned to stone before even getting the first attack against these latter types). In a standard D&D game, these monsters may of course get none or more than one such attacks, depending on player knowledge and preparedness, etc.; but I think that the one free entry attack is a fairly good zero-level model.

Mummies: Mummies are surprisingly weak in this analysis; they are assessed at EHD 6 (one more than their HD of 5), which arguably should put them one monster table lower than in the book (all the other monsters at table level 5 have EHD 8 or above). Their long-term rotting disease is simply not a factor within a single melee. While it requires magic to hit them, I think we would agree that most fighters of this level should have at least one such weapon. While Vol-2 says of such weapons, "bonuses are at one-half value against them", that would be a totally negligible difference (maybe 1 pip in most cases), so instead I implemented the Monster Manual text that they do "one-half normal damage" (i.e., a straight 50% reduction in all damage). It turns out that even this defense is not a large factor, because at this level the fighter is reliably hitting, and the mummy does not have any truly threatening attack to stop them within the scope of the melee.

It sort of makes some sense, then, that later publications bolstered the mummy by adding to its abilities. At the end of Sup-II Blackmoor, Dave Arneson has a section on "Disease" in which he really lays it on, calling the mummy ability "Advanced Leprosy: ...  If  not cured within three days, there is a 95% chance of fatality, with a 2% decrease each successive day. Any character that  succumbs to this dread disease may NOT be raised from the dead; they are permanently dead" (as opposed to the Vol-2 rule which only slows down healing; although the table here instead specifies a 60% chance of irreversible death; but by item (f) causes a loss of 6 Strength points per day, maybe?). Gygax in the AD&D Monster Manual likewise makes the mummy rot potentially fatal (although in 1-6 months time; slowing natural healing as before, but negating all curative spells; and causing permanent Charisma damage), increases attack damage, gives fear and revulsion on sight (that causes paralysis), as well as standard undead immunities to sleep, charm, hold and cold. Another thing that I'm not modeling here is their extra-vulnerability to fire (which wouldn't make any difference anyway, because Arena fighters are not so equipped).

So in theory the mummy value might go up depending on your evaluation of the mummy rot risk (which might make a character potentially more vulnerable in some later encounter, or actually put them in the ground permanently), the implementation of fear and revulsion from AD&D, or possibly down because of the fire vulnerability (esp. when you have pyro-magicians as party members). Personally, the Arnesonian irreversible-death-gotcha has a certain roguish wit; but in my games with no Clerics, perhaps the divide-all-healing-by-10 rule originally in Vol-2 is sufficiently dreadful to be worth a significant EHD/XP bonus (e.g.: say results from a 1d6+1 healing potion get divided by 10 and rounded to the nearest integer; then you'd need a natural roll of at least 4+1, a 50% chance, to get even a single hit point back; so PCs in my games would be practically never able to heal again after an encounter with a Mummy, yowch!). Somehow I like that better than pulling strings to make sure a cure disease is always available before the clock runs out with the insta-death rule.

Giants: Only the Hill Giant is normally simulated in my program ("Hill Giants are the most common (60%)", per Vol-2). While they get a free stone-throwing attack in the Arena before melee, and 2 dice of damage in any attack, this doesn't make that much difference; their EHD is only 8, the same as their HD 8 (so: no XP bonus), in line with other humanoids. While they are on the top Level 6 table in OD&D, this analysis puts them one level lower that, equivalent to the weakest monsters on the Level 5 list. Perhaps if I had randomized among all the different Giant types, the average EHD would be a bit higher, but I don't think even that would legitimize their being on the Level 6 list. Without any save-or-die powers, they would be the odd man out there.

Basilisks: Here's another type that sits on the Level 6 list in OD&D, which the simulator would put on Level 5 (HD 6, EHD 8) -- perhaps a bit surprising. Now, here's the assumption I made for Gaze attacks in the Arena: the monster (such as a Basilisk) automatically gets one such gaze as an entry attack; so the fighter must save-or-be-petrified (thus instantly hors de combat) before joining melee. Afterward, we assume that the fighter is crafty enough to "avert their gaze", taking a −4 penalty hit from then on, but not being subject to any more gaze attacks. Granted that the Basilisk bite attack does only 1 normal die of damage in any ruleset, it's then hard for them counter the abilities of a high-level fighter.

But what this discounts, as we noted at the top of this post, is the game situation where a whole party of PCs turns into a cave and the gaze attack instantly wipes out, say, half of them before the fight even gets started. That area-attack-style capability certainly warrants adding some more EHD (and XP) to their rating. But even if we roughly double their HD from 6 to 12, that still argues for their being a Level 5 monster, not Level 6. (We'll see a more specific result for that in the upcoming Arena v.108.)

Edit: Looking more closely at the OD&D Basilisk description, I see that I've missed a key trait: "it has the power of turning to stone those whom it touches and those who meet its glance". The "touch" ability was removed by Gygax as of the AD&D line (1E, 2E, 3E, etc.), although it still appears in the Basic D&D line (Holmes Basic, Cook Expert, Allston Rules Cyclopedia). My memory of AD&D made me overlook this touch power and it wasn't simulated here; I should do that for the next cycle. It's pretty easy to guess that this will safely justify it being in the 6th level monster list.

Medusa: Now, the other petrifying-gaze monster, the Medusa, has a few less hit dice than the Basilisk, but a much more potent secondary attack: save-or-die Poison by virtue of its venomous snaky tresses. So an opposing fighter must save-or-die before combat even begins, and then again every time a hit is made. The Monte Carlo method tells us that this is a much more potent combination; from a HD 4 base, the Medusa is measured at EHD 12; a jump of +8 points, that is, triple the base HD (and so quite sensibly, triple XP), the highest such ratio among all the monsters measured (excepting a few questionable cases at the very end). This puts the Medusae at the top-end of Level 5 (where OD&D put them) in our analysis; arguably they should go in Level 6 instead. Perhaps an elegant adjustment is to just switch the entries of the Basilisk and Medusae in our tables.

How do you run your mummy rot -- as in Vol-2 with slowed healing only, or with Arnesonian creeping-death-in-3-days, or later Gygaxian death-in-d6-months? And are you prone to forget that Basilisks have petrify-on-touch in OD&D, like I did?


  1. For basilisks we always played it that its gaze is whether the basilisk can see you, not whether you look in its eyes...so it's save vs. stoning every round. You need to cover its eyes or use magical darkness to deal with the gaze.

    1. Yowch! That's a harsh ruling. I guess I've always worked under the assumption that the following paragraph about Medusae applies to both types: "It is able to turn those who look at its eyes to stone" (Vol-2, p. 10).

      However: Looking more closely myself, I see that I overlooked a key part of the OD&D Basilisk description; see the edit above.

    2. I kind of get the feeling that they took away the touch attack to keep a clear and distinct "pecking order" among the petrifying creatures - with it, they would rivals Medusa in deadliness, but without it there's a clear progression of deadliness from Cockatrice to Basilisk to Medusa to Gorgon.

      Also, while not relevant to this particular post, it's interesting that 2E gave it back its deadly touch... sort of. They forked the monster into Lesser Basilisk and Greater Basilisk. The Lesser has only the gaze attack, and is fully vulnerable to having its gaze reflected back at it. The Greater, on the other hand, has poisonous claws and breath (not a breath weapon, just a continuous exhalation within 5 feet of its mouth) and is 90% resistant to the mirror trick.

    3. Right, I did just notice that with the Greater Basilisk in 2E, good observation.