Thursday, September 24, 2020

The Sweet Spot

My ongoing House of Worms campaign uses the 1975 Empire of the Petal Throne rules. As you probably know, these rules are perhaps one of the earliest examples of Dungeons & Dragons house rules ever published. That is, on a fundamental level, EPT is not merely compatible with but wholly derivative of OD&D, at least when it comes to game mechanics. Take a look at the combat matrices, to cite just one obvious example, and what you'll see is identical with what's in Men & Magic. This is not a criticism and it's this continuity with the mechanical conventions of OD&D that make Empire of the Petal Throne the hands-down best choice for introducing newcomers to M.A.R. Barker's world of Tékumel.

At the same time, there are many, many divergences from OD&D in EPT, some small, some large. Among the bigger changes are the way the game handles experience points and leveling. Take a look at the two charts I've reproduced in this entry. Section 630 includes the XP charts for the game's three classes: warriors – here called "fighting men" – priests, and magic-users. This reproduces pre-Supplement I OD&D. A close examination of the particulars reveals differences. Priests requite more experience points to level than do OD&D clerics, while EPT magic-users require less than their counterparts. What you'll see is that, for the most part, all three EPT classes use the same XP charts, that of the fighting man from OD&D (though, interestingly, EPT magic-users need fewer XP than the other two classes at high levels.

Experience points in Empire of the Petal Throne are obtained

in only two ways: (a) acquiring treasure (gold – or other items which can be exchanged for gold Káitars), or (b) slaying hostile beings. No points are granted for casting spells or other types of activity.

This is identical to the approach of OD&D. A key difference is that EPT opponents are only worth 50 XP per hit die rather than the pre-Greyhawk value of 100 per hit die. There is no consideration of the difference between level of character and the level of the monster for this calculation as in OD&D. On the other hand, EPT awards XP on an individual basis, with the character who delivers the killing blow being the one who gets all the experience, regardless of how little damage he might have done. (This is a rule I do not use in my House of Worms campaign) 

This brings us to Section 620 above, which introduces another change from OD&D. Rather than looking at the relative difference in level between a character and a monster for determining an XP award, Barker instead introduces a blanket reduction in XP gain from all sources, starting at fourth level. This reduction increases by steps every two levels thereafter, until, at tenth level, a character counts only 5% of the XP gained toward his advancement.

Taken together, all of these changes, big and small, to the OD&D approach to experience points produces something that, in my experiences, prolongs the "sweet spot" of play. While there's disagreement over precisely where the sweet spot lies, there seems to be a widely held belief that there are a range of levels in D&D-style gaming that are the most congenial to the right balance of risk versus power. For me, that sweet spot lies between fourth and eighth level, when the characters are sufficiently durable that they can't be felled in a single attack – though, it should be noted, Empire of the Petal Throne has an "instant death" critical hit rule – and yet aren't so potent that death is so far from a possibility that they don't act with caution.

It's quite fashionable in some circles to dismiss XP only for defeating enemies and treasure as retrograde, silly, and un-fun, among other things. To the contrary, what I have found is that, because the characters in the House of Worms game – and, I would suspect, most long-running RPG campaigns – are not forever delving in the Underworld and looting tombs, the rate at which they gain experience points is slowed. While lately the characters have been engaged in the exploration of the Temple of Ages and facing off against its denizens, there have been long stretches of the campaign where they were instead involved in diplomatic negotiations, murder investigations, historical research, marriage arrangements, etc. Weeks or even months have gone by without so much as a twenty-side die being rolled in anger. 

If XP were awarded for "roleplaying" or reaching "milestones" or some other activities, the characters would have amassed more points than they have under the rules as Barker wrote them. I make no claim that this is what he intended when he did so. Nevertheless, the set-up has worked very well, preserving the sweet spot of character power well beyond what would be the case if constant character improvement were the order of the day. I am immensely happy with the way Empire of the Petal Throne's experience system works in practice, as are my players. I think it's evidence in favor of preserving OD&D's awarding of experience only for monsters and treasure. 


  1. This seems unnecessarily complicated though. If the goal is to delay level advancement, why not just increase the XP requirements? Why add the extra step of reducing XP earned?

    This might be a convenient place for a house rule to produce a new XP table that advances at Barker's preferred rate, but without needing to do long division on every XP award. (Personally, if I were drawing up those tables, I'd make them the same for all 3 classes, since the only divergence now is for the highest level wizards, but you could also leave that quirk intact.)

    1. I agree that it's strangely complicated; I am still attempting to puzzle out why Barker chose to implement things in this way.

  2. Interesting! I too like it when the campaign gets to the point where the players activities move beyond the xp granting "killing things and taking their stuff". I always find my players still want xp - how do your players feel about long stretches with limited xp?

    1. They're fine with it. The characters still advance, but it's social advancement within the setting. For example, one of the PCs is the governor of a colony, while another is the clan master. Others meanwhile are busy making alliances with powerful NPCs or acquiring ancient lore, etc. The focus is less on improve their characters' game stats and more on improving their place within Tsolyáni society.

  3. This is pretty fascinating. I read EPT (a while back) but I've never run it. I forgot these particular idiosyncrasies of the advancement system. Recently, I've been using straight By The Book OD&D, and I can see how 50xp per HD (and the later XP reduction) isn't a terrible tweak. And it seems quite a bit LESS complicated (and more straightforward) than OD&D's "proportional-XP-based-on-relative-level-versus-HD" system, which attempts to accomplish the same slowdown action as levels progress.

    [of course, the good Professor Barker *could* have just factored the math into the XP charts...if you only earn 5% x.p. at 10th level, doesn't that simply mean you need 20X the listed number of experience?]

    I find it quite appropriate to make clerics a slower advancing class than magic-users: I see a lot of ways this makes sense both in the fiction/fluff, and in terms of "game balance." I've always assumed the reason for fast clerical advancement in D&D was in aid of "party survivability" (you need those healing and raise dead spells!), but they become quite powerful, quite quickly (especially as landholding barons). With a couple checks on M-U's spell acquisition I can certainly see allowing them speedier advancement...all you really lose is the image of the ancient, wizened enchanter (which might not be suitable for EPT anyway).

  4. This XP system is supposed to prevent characters from advancing by grinding vs low-level challenge adventures. Since the XP given by enemies grows linearly rather than exponentially, this makes the level gain become extremely slow at higher levels. Could have been baked in other ways, but he wanted to keep the math simple I guess.

  5. I like how the game uses roman numerals for the levels. It somehow makes the advancement more meaningful. They are not just adding +1 to the level.