11
May
10

the challenge of challenge ratings?

I must be a higher-level blogger than you to be using these rules

May 11, 2010: James finds Masters Set useful for first time in 25 years

In trying to figure out the most profitable monsters to raid, I got the bright idea to index the mean treasure values against the expected “difficulty” of the raid.  I made a stab at doing this, and have bogged down.  How do you determine how tough a bunch of monsters are?

Obviously this will depend hugely on the Dungeon Master, there aren’t really any rules in Dungeons & Dragons, there’s no such thing as an average party, etc. etc.  But from a player’s point of view, sizing up your opponents is a problem of immediate application, especially in a West Marches style game where players can zip all over the landscape looking for (or hoping to avoid) certain enemies.

Aside from the de rigeur objections, there’s a ton of data about how hard monsters are to fight, at least in comparison to each other.  We’ve got zillions of pages about various monsters, their hit dice and number appearing, their likely combat tactics, their special abilities and special defenses, and in some cases the conditions of their lairs.

My initial thought was to multiply average hit dice per average number appearing.  It’s simple and sensible enough for “normal” monsters, and even kind of informative.  For example, it suggests that a decent-sized lair of Orcs (35 @ 1 HD, plus about 5 HD of leaders; average gold per hit-dice of 100 gp) is considerably more trouble than a typical lair of Ogres (7 @ 4 HD; average gold per hit-dice of 71 gp), but more profitable too.*

Obviously the trouble would be how to account for special abilities.  A Dragon Turtle (1 @ 30 HD) in its lair is certainly far tougher than a gang of Neanderthals (25 @ 2 HD, plus some leaders) in theirs.

I’m tempted to use XP values (conveniently listed for each monster in Mentzer BECMI) as a measure of toughness, which is somewhat better but still less than ideal as there are all kinds of weird results in Mentzer.  For example, a 10 HD Red Dragon (AC -1, fire breath, three melee attacks, spells, flight) is worth 2300 XP, the same as a 13 HD Cyclops (AC 5, throw rocks, one melee attack, no depth perception).

Mentzer adopts a more convoluted approach in the Master Dungeon Master Guide, page 9, which I’ll simplify somewhat – feel free to seek out the source for fiddly details:

  1. Total up all the levels in the party.
  2. Total up all the monsters’ hit-dice. For each asterisk, add half the hit-dice.  So a Red Dragon (10 HD**) would be worth 20 points.
  3. Compare the total levels. If the monsters’ total comes to less than 30% of the players’, then the encounter’s a distraction which mainly bleeds a few resources.  If the monsters’ total is about 50% of the players’ levels, then the encounter is a decent fight.  If it’s 70% of the players’ levels, then the encounter will be quite challenging, requiring good play and some luck to overcome.  Up to 90% and it’s probably a climactic encounter which might skrag a character or two.  Much higher than that, the encounter may prove totally overwhelming.

For reference to any Red Boxers reading this, the Grey Company in Tavis’s White Sandbox game typically fields at least eight PC’s, probably average level 4.  This implies that we should be able to defeat that Red Dragon if we’re sharp.   I have my doubts about that, but we should be able to kick a lone Cyclops’s ass without much trouble, and that sounds right to me.

I’ll fiddle with the numbers and see if anything ends up making an acceptable amount of sense.

Anyway, in the meantime: what’s the best way to determine how hard a fight should be?

* I’m tempted to rate all profitability in “Orc-loads,” referring to the approximately 100 gp per lair-hit-die as a standard unit of measurement.  A single Kobold is 0.0114 Orc-loads.


11 Responses to “the challenge of challenge ratings?”


  1. May 11, 2010 at 7:59 am

    Interesting stuff, reminded me of something I’d read recently. Don Turnbull had articles is White Dwarf 1 and 2 where he was trying to come up with a measure of a “monster’s relative malignity.” He called his system Monstermark.

  2. 2 1d30
    May 11, 2010 at 4:29 pm

    I’ve come across this problem too. I suspect most DMs have.

    The first point I want to make is that the “total PC HD and total monster HD, compare” only works when the mean monster level is very close to the mean PC level.

    That is, say you have 6 PCs of 5th level each. And you have 6 monsters of 5 HD each. That is a pretty close fight. Now lower the mean monster HD, and say we have 30 monsters of 1 HD each. Suddenly the fight becomes a lot easier, for various reasons.

    For one thing, a monster can be removed from play by dealing 1 HD of damage to it, reducing the offensive capability of the whole enemy force. But you don’t see a force reduction in the even fight until you deal 5 HD worth of damage to one of them.

    Second, each monster gets its own attack, and in total the damage for 30 monsters of 1 HD may be greater than 6 monsters of 5 HD. But because the 1 HD monsters hit far less often, and not all of them get to attack every round due to maneuvering, the end offensive capability is much lower.

    Third, low-HD monsters are far less likely to have special abilities, and those abilities will be less powerful. Low-HD monsters tend to have lower AC, on average (this would be interesting to graph).

    The inverse to all of this applies when you raise the mean monster level. Take our party of 6 5th level PCs, and pit them against a single 30 HD monster. Or even three 10 HD Red Dragons. The outcome is pretty clear – and gruesome.

  3. 3 1d30
    May 11, 2010 at 4:48 pm

    My second point relates specifically to special abilities. An individual monster may have a special ability far outside what you’d expect based on its HD.

    For example, a Dragon gets a breath weapon, which is an area effect attack that deals hefty “save for half” damage. This means if it catches a lot of PCs in the area it will deal a huge amount of total damage in one round. And since the monster is smart, and is found individually and in a large space, it is usually smart enough and able to maneuver to strike multiple targets. So the dragon’s breath should represent a huge difficulty boost.

    Likewise, there is an enormous difference between 10% magic resistance and 50%. But how do you track a +5 save vs magic agianst a 25% magic resistance? I’d tend to count MR as worth double that of a save vs magic, since so many spells offer no save and the MR is a second chance rather than a modifier. So I’d value a +2 vs magic the same as 5% MR.

    Poison (of the save or die variety) is a huge issue, but its value is dependent on the monster’s ability to hit in the first place. This is one place where many small snakes can be very nasty. If each 5th level PC is AC 0 on average, and the snakes have a 5% chance to hit, you’ll see on average 1.5 poison saves per round among the party. With 6 snakes of 5 HD, each snake has a 25% chance to hit, so you see the same average 1.5 poison saves per round. With 3 snakes of 10 HD, each has a 50% chance to hit, so again you see an average of 1.5 poison saves per round. Based on that, compare an encounter with 30 fish of 1 HD against the 30 snakes of 1 HD. The snakes have a poison ability, so they offer extra difficulty. That poison difficulty number, translated into XP award, should be the same number regardless of the HD of the snakes. All that matters is the total HD of the opposition.

    Being immune to nonmagical weapons is a huge benefit, but only against PCs who don’t have them. It’s a binary difficulty, although you could argue that some PCs have magic weapons and some don’t. But it appears that the very first +1 is the most important – it separates the creature from the vast breadth of attackers. The creature becomes totally immune to Orcs, Giant Rats, and even the smaller poisonous monsters (anything under 4+1 HD if I recall correctly). A Gargoyle immune to nonmagical weapons could enter a farming village and kill everyone without taking a scratch of damage. Or an entire Orc village, of over a hundred Orcs (just avoid the king and the shaman!). But a single Ogre would be an uncertain fight.

  4. 4 1d30
    May 11, 2010 at 4:55 pm

    Another horrible special ability I found recently was the Strength-draining of the Shadow.

    When a Shadow hits, it causes 1d4+1 Strength damage. If you drop to zero STR you die and become a Shadow.

    Shadows are low HD, and so they don’t hit especially often. And their AC is not especially good. And they can’t even touch you if you bear a light source.

    But they can hide on the edges of the light and pounce on someone as soon as they aren’t lit anymore. This limitation is especially nasty because it forces them to use the best possible tactics, focusing on a single PC until he dies.

    Their damage is the scary part. Effectively, it doesn’t matter what your HP are, they kill you at zero STR. So the average STR damage is 3.5, and the average PC strength is 9. This means three Shadow hits will kill most characters, though Fighters may take four or even five.

    But a crowd of Shadows (2d10, they come in large packs), attacking a lone PC in the darkness, are going to completely tear him up. And then he turns into a Shadow and the pack has one more member.

    This special ability is pretty awesome, and it’s actually more powerful than a save-or-die effect. Because it’s effectively “no save, one third of a death”, high-level PCs are safe only if they have exceptionally high ACs.

    Or if they stay in the light.

    But often, you won’t know that Shadows are near until they attack. And nobody can see what happened to the struck character, because he was in darkness at the time. And typically the characters who stay in darkness are the ones with dark-vision …

  5. 5 1d30
    May 11, 2010 at 4:59 pm

    Then of course there are the special abilities that don’t actually come into play. Let’s say you have a fairy creature that can cast Rock to Mud, but it is encountered in the forest. The ability cannot come into play, so the encounter will be easier.

    Player knowledge comes in for monster defenses, so that muddies the waters. But a golem immune to fire isn’t any more difficult for it if the PCs don’t have any fire to use on it in the first place.

    Or a flying creature encountered inside where it can’t escape the reach of the PCs.

    And certainly every ability that remains unused when the creature is slain.

    Not that this would change the XP award. But it does change the difficulty of the encounter.

  6. 6 James
    May 11, 2010 at 5:08 pm

    That analysis of the Shadow is great! I always loved those guys and now I now why. As if the Thief didn’t have enough to worry about…

    Regarding post #3, one problem with any flying creature immune to non-magical weapons is that it can always take to the air and most parties will have relatively few magical arrows or bolts to bring it down. A fire-breathing Gargoyle would be pretty horrible.

    Regarding #5, it’s probably a safe assumption that if monsters are going to show up, they’re going to show up in a context that puts their abilities to respectable use, unless the players think of some clever way to fight them in a different context.

  7. 7 James
    May 11, 2010 at 5:15 pm

    Incidentally Shadows aren’t as dangerous in Moldvay’s (and Mentzer’s) Basic Set: though they surprise 83% of the time they only drain 1 point of Strength per hit. On the other hand, there’s no mention of them staying out of the light, although I do think that’s a very sensible rule to make them a little less deadly.

  8. 8 Charlatan
    May 13, 2010 at 2:50 pm

    My general gaming knowledge, I fear, doesn’t really measure up to the thread (or even the blog!), but I wanted to make an observation about #2 and the 30 orc scenario:

    It feels like tyranids! Your points about the orc logistics are really crucial, because a situation in which the orcs all win initiative, pop out of nowhere and attack whichever PC isn’t wearing armor… I suspect the last of the 30 orcs ends up dead at the hands of a fighter, but it seems like the math is there for them to kill a clothy and 1 more. God help the players if the orcs are archers!

    I vaguely remember the AD&D combat tables having some special rules for multiple attacks against 1hd baddies, and this must be why.

  9. May 14, 2010 at 10:17 am

    James, please drop me an email; I’ve been trying to contact you through other channels to no avail :) sjohn@io.com


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