Sometimes it takes years for your brain to puzzle things out.
For example, I wrote Revisiting Encounter Design way back in 2008. The basic thesis was that you should generally abandon the new wave fetish for My Perfect Encounters(TM) and embrace a more flexible method of encounter design that would emphasize faster-paced, strategic-based play.
The four major tenets I argued for looked like this:
(1) Design most 3E encounters around an EL 2 to 4 lower than the party’s level.
(2) Don’t be afraid of large mobs (10+ creatures) with a total EL equal to the PCs’ level. The common design wisdom is that these creatures are “too easy” for the PCs. This is true if you’re thinking in terms of the “common wisdom” that sprang up around misreading the DMG, but in practice these types of encounters work just fine if you’re looking for fast encounters and lots of them.
(3) Encounters with an EL equal to the PCs’ level should be used sparingly. They should be thought of as “major encounters” — the memorable set pieces of the adventure. It actually won’t take very long before the expectations of your players’ have been re-aligned and these encounters leave them thinking, “Wow! That was a tough encounter!”
(4) And that means you get even more bang for your buck when you roll out the very rare EL+2 or EL+4 encounter.
(The general philosophy of this advice, it should be noted, is widely applicable beyond D&D. In Feng Shui, for example, it means “keep a healthy supply of mooks flowing through your scenario.” In Shadowrun it means not letting a ‘run bog down into a single giant melee; keep the action on the hoof by making it possible for the PCs to cut their way rapidly through waves of security. And so forth.)
Most people seem to have grokked what I was selling. But there was a smaller group of people who insisted that I was wrong: That if they built an encounter with sixteen CR 2 creatures that the PCs would take a lot more damage than if they used a single CR 10 opponent. In fact, I still get fairly regular e-mails to this effect six years later. And I could never figure it out: Running the math on hypothetical scenarios regularly confirmed what years of play and hundreds of game sessions had taught me. It certainly wasn’t impossible for the mob of CR 2 creatures to out-perform the CR 10 creature, but in general the fighter was going to rapidly cleave through the mooks or the wizard’s fireball was going to rip them apart.
Were the people e-mailing me fudging dice rolls to toughen up the weaklings? Did their players just have no idea how to use mass damage or area control spells?
Nah.
It took six years, but then I was driving down a highway in Wisconsin the other day when epiphany finally hit me: These are reports of anecdote. And the problem with anecdote is that it selects for the exceptional and the unusual.
You don’t remember the 19 times that you used a CR 10 monster against a 10th level party and it took a few rounds to take it down while tearing out a few large chunks of hit points from the group. Instead, you remember the time that the party faced a single tough opponent and miraculously chopped his head off in the first round of combat.
Similarly, you don’t remember the umpteen times that your wizard casually fireballed a group of mook orcs and cleared ’em out without any hassle. What you’ll remember is that one time that a horde of kobolds left the PCs screaming and fleeing in terror.
It’s also likely that the actual numbers aren’t actually being looked at in these anecdotes: “Remember that time that the six orcs in area 4 were a lot tougher for the party to take out than the demon in area 10?” Sure. But were those actually EL equivalent encounters? Or were the orcs all CR 8 (for an EL 13 encounter) while the demon was CR 10?
None of this is a problem, of course, unless you start using the exceptionalism of your anecdotes as a guiding principle of scenario design. You want your scenario to be exceptional, of course, but you won’t achieve that if you’re expecting the statistically exceptional in every encounter.
(Of course this is another advantage of the encounter design method I advocate for: By increasing the number of encounters experienced, I increase the number of opportunities for the memorably exceptional moments to happen. Sometimes that will be the result of improbable math; sometimes it will be the result of clever and unexpected play. That’s the beauty of a non-deterministic medium.)
Interestingly, the “many weaker monsters” appears to be the preferred encounter design for D&D5.