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| Roger Moore battles to the death with the AD&D XP calculation rules, Dragon #89 |
I've been working on a little project for my home game which has had me taking a deep-dive into the AD&D experience point system. I thought I'd share some of the system's strengths, errors, weaknesses, and other interesting bits (presuming you're the type of weirdo system wonk that finds this sort of thing interesting, I should say).
On average, monster XP was always secondary to treasure XP in old-school D&D. That doesn't mean that some thought wasn't put into how to generate XP values for monsters, however. To see how 1st edition handled XP, you'll need the DMG: specifically, p. 85 (Experience Points Value of Monsters table) and pp. 196-215 (Appendix E: Alphabetical Monster Listing).
So, you look up the creature's Hit Dice, apply the appropriate Basic XP Value, and then start adding less expensive SAXPBs and more expensive EAXPAs, each representing some sort of special ability the creature has, until you arrive at the final total. The Hit Dice for the creature also determines how much XP per hit point the creature is worth, an amount added on top of the base creature value. So, a 6-HD creature isn't just worth, say, 350 XP, but instead 350 + 6 xp per hp--on average, more like 377 XP.
Calculation Issues
If you dive in and start trying to reverse-engineer the XP values given in the DMG Appendix, you'll soon start running into trouble. As a result, I've seen some arguments that the Appendix doesn't actually use the p. 85 method: that the method is merely a means of calculating XP for your own monsters, and that the Appendix does its own thing. However, having gone through all the monsters in the Monster Manual and Fiend Folio, I can guarantee that Appendix E definitely uses the p. 85 rules: the number of values impossible to calculate using that method is a mere handful, versus the dozens that work out correctly. You just need to take a very careful look to work out some of the kludges the designers used.
Arbitrary Values
One place where confusion and natural skepticism creeps in is that the Appendix often arbitrarily assigns SAXPBs and EAXPAs to arrive at its monster totals, despite (or in addition to) the footnoted guidelines for those on p. 85.
A good example is the hydra. Look at its breakdown:
|
5 HD/IV |
SV: D11/P12/R13/B13/S14 |
165+5/hp |
|
6 HD/V |
SV: D11/P12/R13/B13/S14 |
275+6/hp |
|
7 HD/V |
SV: D10/P11/R12/B12/S13 |
400+8/hp |
|
8 HD/VI |
SV: D10/P11/R12/B12/S13 |
650+10/hp |
|
9 HD/VI |
SV: D8/P9/R10/B9/S11 |
1,000+12/hp |
|
10 HD/VII |
SV: D8/P9/R10/B9/S11 |
1,500+14/hp |
|
11 HD/VII |
SV: D7/P8/R9/B8/S10 |
2,150+16/hp |
|
12 HD/VII |
SV: D7/P8/R9/B8/S10 |
2,850+16/hp |
(Interestingly enough, the DMG gives values for up to 16 heads, but by the Monster Manual a hydra tops out at 12 heads, even if using the Lernaean variant that grows extra heads).
If you compare the 11-HD version and the 12-HD version, you get a noticeable XP value increase. However, by the p. 85 table there's no reason to do this. They're both in the same HD category (11 to 12+), and no new special abilities are gained at 12 HD that, by the footnotes, would appear to justify a higher XP value. They even have the same saving throws. However, a 12-HD hydra does get an extra attack (hydras have 1 attack per head), and it uses the next higher attack matrix column for all 12 attacks (because it's 12 HD). Neither is specifically listed in the special abilities section, but if you compare the 11-HD and 12-HD values, the difference in their XP values is exactly 700. This might seem rather arbitrary, but checking the p. 85, you can see that 700 is the SAXPB value for the 11-12 HD range (700 XP). The designer didn't pick any random number, but selected the right modifier for the creature's HD range to represent this combat capability, and more importantly to make it so that the two variants didn't have the exact same base XP value despite being noticeably different. As such, an 11-HD hydra can be calculated out as:
1,300 Base + (0) SAXPB + (1 x 850) EAXPA = 2,150+16/hp
And a 12-headed hydra works out like so:
1,300 Base + (1 x 700) SAXPB + (1 x 850) EAXPA = 2,850+16/hp
So it's not that the math doesn't work, but that the designers just used the math as they felt the need to. The fault lies more with the incomplete footnotes than a true inconsistency, since the additional cost is clearly warranted and follows the established pattern.
Composite Values
The DMG does not provide XP values for every possible iteration of every creature. The idea I'm sure was to save space (and time), since otherwise the appendix would be noticeably larger. For example, boars in the DMG have three XP entries, but need eleven to do the whole range as presented in the Monster Manual. Unfortunately, when one or a handful of XP values are given to represent a wider range of possibilities, how those summational values are generated is inconsistent, using one of two different methods, which might lead people to think again that the p. 85 method isn't being used. But it still is: just in arbitrary fashions.
The first method is when the Appendix just takes one valid value and uses it to represent the whole range. For example, the Barracuda is given a single 20+2 XP value, which perfectly represents the XP for its middle-range example: a Barracuda can have from 1 to 3 HD, and the given 20+2 XP value is what the 2-HD example would have (the others, unstated in the Appendix, would be 10+1 for 1 HD and 35+3 for 3 HD).
The second method is when the Appendix creates a composite value, a rough average for the whole creature range. They tend to have a base value fitting one element of the range, coupled with a XP per hp value from a different part of the range. For example, the Sea Horse's singular 20+4 XP value is impossible using p. 85, but when taken as a stand-in for all three of its HD possibilities it has the base 20 XP value from the low end (2 HD) and the 4 XP per hp value of the high end (4 HD).
The DMG doesn't explain which method it uses for any given entry: the only way to figure this out is to calculate XP for individual subentries yourself, using the p. 85 methodology. It doesn't even say that these are averages of one kind or another, you need a copy of any of the rare Monster Cards sets for such a note ("Average value only, see DMG p. 85"). But regardless, the values are consistent with p. 85.
HD Pluses
The p. 85 table says you have to take HD pluses into account. For example, there's a "6+1 to 7" category, so we know that 6+1 is treated different than a straight 6 HD. However, the table doesn't appear to say precisely how. Creature can have some pretty high pluses at times (e.g. the Type VI demon at 8+8, or the all-time champ mezzodaemon at 10+40). And, if you know your 1st edition, you know that the DMG treats Hit Dice pluses differently depending on the situation.
For example, for saving throw purposes, pluses in hit points move a creature steadily upwards in Hit Dice. +1 hit point raises it one HD level for saving throw purposes. Every 4 full points beyond that raises it another Hit Die: e.g. +5 raises it two HD, +9 raises it three HD, and so on.
For attack purposes, however, while any plus of 4 or higher equals an additional Hit Die, this doesn't scale. So, if you've got a monster with 4 HD, 4+1 to 4+3 does nothing, while anything from 4+4 to 4+100 gets you the same result: treat as a 5-HD creature. And as a 5-HD creature uses the same column as a 4-HD creature on the attack matrix, it's pointless. So, the only creatures that benefit are those with a) odd HD values (since advances on even ones always just bump you up within the same attack matrix column), and b) with a bonus of +4 or higher. Only a handful of canon creatures actually have this.
This does make one naturally ask which of these methods the monster creation system uses, or if it uses either of them at all. Checking out the creatures with high HD pluses in the Appendix as test cases, we have:
Bear, Brown: HD 5+5. Saves: 7 HD. Attacks: 6 HD. XP: 300+6/hp (5+1 to 6 HD).
Bear, Cave: HD 6+6. Saves: 8 HD. Attacks: 6 HD. XP: 475+8/hp (6+1 to 7 HD).
Demon, Type V: HD 7+7. Saves: 9 HD. Attacks: 8 HD. XP: 3,000+12/hp (8+1 to 9 HD).
Demon, Type VI: HD 8+8. Saves: 10 HD. Attacks: 8 HD. XP: 3,600+12/hp (8+1 to 9 HD).
Devil, Horned: HD 5+5. Saves: 7 HD. Attacks: 6 HD. XP: 1,320+6/hp (5+1 to 6 HD).
Devil, Erinyes: HD 6+6. Saves: 8 HD. Attacks: 6 HD. XP: 875+8/hp (6+1 to 7 HD).
Gargoyle: HD 4+4. Saves: 5 HD. Attacks: 4 HD. XP: 165+5/hp (4+1 to 5 HD).
Intellect Devourer: HD 6+6. Saves: 8 HD. Attacks: 6 HD. XP: 1,510+8/hp (6+1 to 7 HD).
Lammasu: HD 7+7. Saves: 9 HD. Attacks: 8 HD. XP: 850+10/hp (7+1 to 8 HD).
Mind Flayer: HD 8+4. Saves: 9 HD. Attacks: 8 HD. XP: 1,800+12/hp (8+1 to 9 HD).
Nightmare: HD 6+6. Saves: 8 HD. Attacks: 6 HD. XP: 600+8/hp (6+1 to 7 HD).
Sahuagin Baron: HD 6+6. Saves: 8 HD. Attacks: 6 HD. XP: 350+8/hp (6+1 to 7 HD).
Sahuagin King: HD 10+10. Saves: 13 HD. Attacks: 10 HD. XP: 1,350+14/hp (9+1 to 10+ HD).
Salamander: HD 7+7. Saves: 9 HD. Attacks: 8 HD. XP: 825+10/hp (7+1 to 8 HD).
Scorpion, Giant: HD 5+5. Saves: 7 HD. Attacks: 6 HD. XP: 650+6/hp (5+1 to 6 HD).
Shedu: HD 9+9. Saves: 12 HD. Attacks: 10 HD. XP: 1,950+14/hp (9+1 to 10+ HD).
Spider, Phase: HD 5+5. Saves: 7 HD. Attacks: 6 HD. XP: 700+6/hp (5+1 to 6 HD).
Su-Monster: HD 5+5. Saves: 7 HD. Attacks: 6 HD. XP: 225+6/hp (5+1 to 6 HD).
Troll: HD 6+6. Saves: 8 HD. Attacks: 6 HD. XP: 525+8/hp (6+1 to 7 HD).
Umber Hulk: HD 8+8. Saves: 10 HD. Attacks: 8 HD. XP: 1,300+12/hp (8+1 to 9 HD).
Wyvern: HD 7+7. Saves: 9 HD. Attacks: 8 HD. XP: 925+10/hp (7+1 to 8 HD).
Xorn: HD 7+7. Saves: 9 HD. Attacks: 8 HD. XP: 1,275+10/hp (7+1 to 8 HD).
The tl;dr on this is that neither the save nor attack methodology works, and a third use for pluses is found instead. The only method that works out (nearly) every time is that if you take the table as its own thing: if you have a plus, no matter how large, it's simply treated as a plus. That is, +1 to +1000 is all the same. For example, a lammasu (7+7 HD) is in the "7+1 to 8" category, and a sahuagin king (10+10 HD) is counted as the "9+1 to 10+" category. Our mezzodaemon, then, is (despite its +40) just placed in the "9+1 to 10+" category. This all makes sense, as it follows the literal text, whereas the other methodologies would require explanatory footnotes that aren't there.
There's only one creature that this doesn't work out with: the Type V/Marilith. Following our pattern, this HD 7+7 creature should be in the 7+1 to 8 HD category, with +10/hp. It's possible to get an XP value of 3,000 using that category, so if you switch the creature to +10/hp, the overall math still works just fine:
7+1 to 8 HD:
375 Base + (4 x 175) SAXPB + (7 x 275) EAXPA = 3,000+10/hp
As such, I'm inclined to treat the Marilith--1 creature out of 22--as an easy-to-make error, and would simply adjust its per-HP XP value down a slight amount to +10 per.
Creatures with Errors
I said earlier that you can use the p. 85 method to calculate the vast majority of creatures in the DMG Appendix, if you're willing to throw about SAXPBs and EAXPAs willy-nilly like the original designers often did. Rather than going through the whole Appendix, which would require a 30,000-word post, I'll just list the creatures that don't work out, why, and what you'd need to do to make them consistent with the rest of the entries. Corrected XP values use the p. 85 methodology to get as close to the canon XP value as possible for that creature's HD category unless specified otherwise. Huge thanks to Algolei over at the Grognard's Tavern for doing the vast bulk of the work I'm using in this section.
Banshee (Groaning Spirit)
2,450+10/hp. As a 7-HD creature, +10/hp is wrong. It should have 2,450+8/hp.
Crocodile (normal)
60+4/hp. As a 3-HD creature, 60 is impossible and +4/hp is wrong. It should have 65+3/hp.
Demon, Type V
3,000+12/hp. As above, as a 7-HD creature it should have 3,000+10/hp.
Devil, Horned
1,320+6/hp. As a 5-HD creature, a value ending in 20 is impossible. It should have 1,325+6/hp.
Dinosaur, Ceratosaurus
600+12/hp. This was calculated as an 8+1 HD creature, but is only 8 HD. Either make it 8+1, or change its XP to 375+10. Normally I favour trying to get to the canon XP total, but the creature is just a hit point sack with no special abilities, and the gulf between the XP value it's given and the XP value it should have is quite large.
Dinosaur, Mosasaurus
1,300+18/hp. As a 12-HD creature, it should have 1,300+16/hp. That's the base value for that HD range, meaning it has no SAXPBs or EAXPAs. Technically it should have an EAXPA for doing such enormous bite damage, but this is an XP adder that is often skipped, I've noticed.
Displacer Beast
475+8/hp. As a 6-HD creature, +8/hp is wrong. It should have 475+6/hp.
Dog, Blink
170+5/hp. As a 4-HD creature, 170 is impossible and +5/hp is wrong. It should have 175+4/hp.
Dryad
105+3/hp. As a 2-HD creature, +3/hp is wrong. It should have 105+2/hp.
Eel (Giant and Weed)
The values for these don't work at all, but make a lot more sense when reversed. This is just largely a transcription error.
That having been said, what should be the Giant Eel value (150+6/hp) also looks to have been calculated as being 1 HD larger than the creature actually is (6 HD instead of its real 5 HD). The creature should have 90+5/hp.
Elephant, Loxodont
2,125+16/hp. As a 11-HD creature, a value ending in 25 is impossible. It should have 2,150+16/hp.
Genie, Djinni (regular)
735+5/hp. As a 7+ HD creature, 735 is impossible and +5/hp is way off. It should have 725+10/hp.
Giant, Storm
5,850+20/hp. As a 15-HD creature, it should have either 5,600+20/hp (closest value under) or 6,150+20/hp (closest value over). Also, while not technically an error, there's a missing value here: Storm Giants have a randomly rolled HD plus (1D6+1). If this plus is 5 or more, then that's enough to bump the giant up to the 17-HD category (and improves both its saving throw and attack matrix categories). These chonky Storm Giants would be worth either 7,000+25/hp (if following the "closest value under" pattern) or 7,650+25/hp (if following the "closest value over" pattern). The Fire Giant also could use such an entry.
Golem, Clay
3,600. A fixed XP value, because its hit points (50) are always the same. Effectively an 11-HD creature (4.5 average hit points per Hit Die, x 11 = 49.5, rounded up to the creature's 50 hit points; this also matches its THAC0 of 10). At 11 HD and 50 hit points, that's (50 x 16) 800 XP just from hit points. Add this to the 1,300 base and you have 2,100 XP, and 1,500 left to account for. The closest you can get to that is 1,550. As such, it should have 3,650 XP.
Golem, Stone
8,950. A fixed XP value, because its hit points (60) are always the same. Effectively a 13-HD creature (4.5 average hit points per Hit Die, x 13 = 58.5, rounded up to the creature's 60 hit points; this also matches its THAC0 of 9). At 13 HD and 60 hit points, that's (60 x 18) 1,080 XP just from hit points. Add this to the 1,800 base and you have 2,880 XP, and 6,070 left to account for. The closest you can get to that is 6,000. As such, it should have 8,880 XP.
Griffon
375+10/hp. As a 7-HD creature, 375 is impossible and +10/hp is wrong. It should have 400+8/hp.
Hydra (6-headed)
250+6/hp. As a 6-HD creature, 250 is impossible. It should have 275+6/hp. This would also change its Dungeon Random Monster Level from IV to V, which you should generally avoid to in turn avoid having knock-on effects with random encounter tables. However, in this case I don't think that's an issue as the 5-headed variant already occupies Level IV, so no one becomes bereft of hydras.
Invisible Stalker
1,090+10/hp. As a 8-HD creature, 1,090 is impossible. It should have 1,175+10/hp. You could alternately lower it to 1,000+10/hp, but that would change its Dungeon Random Monster Level from VII to VI.
Lammasu
850+10/hp. As a 7+ HD creature, 850 is impossible. It should have 825+10/hp.
Lizard, Minotaur
875+10/hp. As an 8-HD creature, 875 is impossible. It should have 850+10/hp.
Ooze, Grey
200+5/hp. As a 3+ HD creature, +5/hp is wrong. It should have 200+4/hp.
Owlbear
225+8/hp. As a 5+ HD creature, +8/hp is wrong. It should have 225+6/hp.
Rust Monster
185+4/hp. As a 5-HD creature, 185 is impossible, and +4/hp is wrong (it looks like it was calculated as a 3+1 to 4 HD monster accidentally). It should have 205+5/hp.
Turtle, Giant Sea
900+10/hp. This one is right out to lunch: it's a 15-HD creature, but +10/hp is the value for a 7+1 to 8 HD creature (which it looks like it was calculated as, with 3 SAXPBs). It's not some kind of weird turtle tax as the value is far less than even its snapping cousin that has a third the HD and worse THAC0. As a 15-HD creature it has a minimum XP value of 2,400. If you assume the 3 SAXPBs given above you would have +3,750, taking the total to 6,150. However, as I've shown above, sometimes adders are given arbitrarily, and so just because it's worked out a particular way at one HD level doesn't mean that it would be worked out the same at all HD levels. Overall, it should have anywhere from 2,400 to 6,150 XP, and +20/hp no matter what. As it has no special abilities, having neither the surprise chance nor the potential 0 AC of its snapping cousin (which has a SAXPB and a EAXPA), I'd be inclined to leave it at 2,400.
Wolf, Winter
245+5/hp. This one is off because the Monster Manual and the DMG have a disagreement going on: the MM says its a 6-HD creature but the DMG Appendix lists it as 5 HD (and calculates its XP total as such). Presuming the MM is right, the creature's value should be 275+6/hp (if you want to be closest to the canon value) or 425+6/hp (if you want to give it the same number of SAXPBs (2) and EAXPAs (1) as the designers did for their 5-HD calculation; I'd note though that there's no reason for it to have anything other than 1 EAXPA for its breath weapon, which returns us to the 275+6/hp figure).
Wolverine (normal)
125+3/hp. As a 3-HD creature, 125 is impossible. It should have either 120+3/hp (if you want to be closest to the canon total) or 105+3/hp (if you want to match the SAXPB and EAXPA distribution used for the giant wolverine).
Again, the hundreds of other entries/subentries work out just fine, so while this might look like a large list, it's just a small fraction of the total. In addition, the changes to bring the creatures in line with the rest are extremely minor.
System Weaknesses
People have used the given XP values for monsters for decades without much of an issue. For all that the values have been arrived at somewhat arbitrarily, there is a combination of systemic implementation and carefully chosen designer fiat that results in what might be described as pleasantly inconsistent consistency. That is, there's fudging, but using a consistent baseline, towards a consistent goal (rough monster parity, and usability at the tabletop).
There's an old saying that there's never enough time to do something right, but there's always enough time to do something over. Having overseen a few lengthy revisions of deadline-compressed game design, I completely agree. The DMG was prepared at great speed, and I have no doubt Gygax (or whomever was in charge of the XP system; I suspect it was Gygax) knew that it was flawed in parts, leading to the note on p. 85:
Judicious application of these guidelines will assume that an equitable total number of experience points are given for slaying any given monster. ... If an otherwise weak creature has an extraordinary power, multiply the award by 2, 4, 8, or even 10 or more.
This is our get out of jail free card, a caveat that says "look, if it's not working as written, just start adding stuff". And knowing that you can just spam adders as desired serves to paper over a lot of the system weaknesses. But it requires someone who knows the system well, and doesn't address all issues.
Ideally, given enough time to polish (there's never enough, thanks to printing deadlines and the general need to keep putting our product to generate income), you get a system with a minimal number of kludges, something that gets you what you need without special rules pleading. But if you can't get there, you should never feel so slavishly bound to firm rules that you ignore the exceptions generated that could break the game in spots. Things like the note above, and the many instances where the DMG Appendix just arbitrarily adds SAXPBs and EAXPAs until it gets to a good number, show that Gygax understood this.
"When we were preparing the monsters included in this issue’'s Creature Catalog, some general tendencies began to appear in the Dungeon Masters Guide system for assigning x.p. values. These have been recorded below for use as guidelines."
The way the above is worded ("tendencies began to appear") makes it clear that Moore was as in the dark as the rest of us as to how to "properly" do things. Similarly:
"The system for assigning x.p. values appears in the DMG on pp. 85-86; the monster level table is on p. 174. Both are quite straightforward, as far as they go. The difficulty is in assigning x.p. values for special and exceptional abilities not described in detail, or not specifically mentioned. Just what constitutes a special or exceptional power?"
Gygax was still at the company in 1984, but likely unavailable for consultation on everyday rules matters, and it's this that makes me think the XP rules were his; otherwise, Moore could just talk to whomever at the TSR offices was responsible (the other possibility that comes to mind is that the XP system designer wasn't Gygax, but was fired in the 1983-84 TSR purges and so also unavailable).
In any case, the article is essential if you want to better systematise your approach to creating XP value, beyond what the DMG itself gives you, though you might not agree with some of the choices the article makes.
Caveats and fudging aside, there are areas where the system does tend to fall down:
- No allowance for halved saving throw values due to Non- intelligence.
- No allowance for magic resistance granularity: 5%-100% is all treated the same.
- Spell use capability is always exceptional, whether it's cantrips or a max level cleric/magic-user combination.
- No allowance for attack matrix increases on their own (e.g. going from 7+1 HD to 8 HD is the same for XP purposes, even though the creature attacks more accurately). For example, by the book, both the 11-HD and 12-HD Ropers have the same XP value, despite the 12-HD version using a better attack matrix column.
- And, most importantly for me, there's no allowance for AC beyond "having AC 0 or better". Two examples of the same creature, but one having 10 AC and the other having 1, will be worth the same amount (the designers would likely have just plugged in an adder in such a case, as we have seen, but all the same, the given guidelines don't cover this area at all). The system should have some kind of scaling AC surcharge, in the same way that there is effectively a scaling for saves and attack matrix capability (even if the latter breaks down at times, it's still roughly accounted for in overall HD progression).
What about the other manuals?
As for doing the system over, I suspect that the XP values given in Monster Manual II were constructed with a modified form, as many of its values markedly differ from the p. 85 methodology in a way that the MM and FF values do not (something for another article). But this new methodology was never released for public consumption, and the system would not be refreshed until 2nd edition was released (and was further modified throughout that edition's life).
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