For a game where attrition is often professed to be important, why has D&D NEVER offered guidance on gauging the challenge of encounters based on said attrition?
Well, they sort of have though, haven't they...?
I mean the 6-8 medium/hard guidelines are exactly that--guidelines--as in guidance. When I first started 5E from an AD&D background, I vastly overjudged what I thought PCs could handle because in AD&D they could handle such encounters. Now, they really can't at the same level.
I decided to work on a summary of my campaign encounters to date. The encounter difficulty distribution of the 77 encounters so far is 30% easy, 15% moderate, 35% hard, and 20% deadly. The (adjusted) XP value for the average encounter is
almost exactly half of the deadly max (so for level 1, that would be 100 xp per PC), with the maximum adjusted XP value at 165% of that barrier between hard and deadly. That means on average my encounters are half of max deadly value, which is the maximum of moderate. In other words, nearly exactly between moderate and hard.
I think it would have been helpful if the designers assigned values to the encounter difficulties:
1 - easy
2 - moderate
3 - hard
4 - deadly
At 6-8 (say 7) moderate to hard (2.5) that gives 17.5 "encounter points". If you spend those points given the values above, with say a short rest about every 5-7 points, it works out well IME.
- In the easy encounters, a few hp might be lost or some ammo spent, etc. but that is about it.
- In moderate encounters, spell slots are typically used but at a minimum, hp is likely reduced, a potion or such might be consumed.
- In hard encounters, spell slots are used, even a big whammie maybe, hp depletion is promenent and wider spread--not just the tanks. Magic items used are likely spent.
- In deadly encounters, everything is on the table. Players understand this is when they have to use resources and recovery (a short or long rest) is likely needed.
You throw two deadly encounters at PCs without any rest in between, and they are likely feeling the sting of attrition. A moderate and hard in tandem and spell casters might start wondering how much they can use a spell slot on the next encounter. An easy follow-up encounter makes the players relax--all in not doom and gloom, but that last medium encounter might just be too much after so many resources are gone.
I (quite literally!) see this sort of attrition-based game play work all the time. But, there is a point I would like to address in that: this is on the "adventure" day--during the actual adventure, not just random encounters while travelling, etc. Travelling days are often much easier as random encounters don't tend to cluster like adventure encounters do, with little chance to rest in between.
I'll give you a summary of the encounters for my last three sessions. The PCs had just discovered the enterance to a cave system where water was flooding from (ruining the region!). We had a scroll of Water Breathing, so had 24 hours to finish the mission before we had to return. For our 4 PCs the encounters were:
Session 1:
1. Two water weirds (moderate)
2. A giant shark and a sahuagin (hard)
3. Two sahuagin priestesses and a merrow (hard)
- short rest -
4. Six sahuagin coral smashers (hard)
- short rest -
5. A Kraken priest (BBEG) and five sahuagin coral smashers (deadly)
- long rest -
Using the above point system: 2+3+3 (rest) +3 (rest) +4 (long rest) = 15. Not guite the 17.5, but close. We could have handled another moderate encounter probably at most without
serious risk of TPK...
Session 2: the players decided to remove the remaining threats to the area
1. Four merrows (hard)
2. Four swarms of quippers (easy, avoided)
3. A water elemental and a sahuagin (hard)
- short rest -
4. Four hunter sharks (hard)
5. Two sahuagin priestesses (moderate)
x. Two merfolk (allied - no point cost)
6a. Two sahuagins (easy)
Session 3: battle resumed after the two sahuagins when their companions came
6b. Four sahuagins and two sea hags -- the merfolk we allied with (hard, resulted in PC death)
- short rest - (we didn't have time for another long rest but we REALLY wanted it)
7. Six sahuagin coral smashers (hard), this used a lot of our last ditch resources like
relentless endurance on BOTH half-orc PCs... The PCs were nearly exhausted of all resources. Now, losing the healer in the prior encounter really made this one hurt.
x. Ten merfolk and four reef sharks (allied - no point cost)
STORY AWARD: finally closed portal
- long rest - (on the surface)
3+1+3 (rest) +3+2+1+3 (rest) + 3 (long rest) = 19. A bit over the 17.5, and we felt it at the 16 point mark! Between the two "adventuring days" for sessions 1-3 above, the total is 34 points, just one shy of the 35 average.
Now, the PCs could have gone in different directions changing the encounter order, and they would have had to adjust the rest schedule to match it--wondering if the next encounter might be too much to handle with their current resources levels.
The "sahuagin lair" was designed around the world implications for the cave system map, random rolls for encounter difficulty (based on the WOLRD, not the PCs!!!, but this is another point not directly connected to the guidelines in the DMG...), and a search to find creatures appropriate to the encounter difficulty, story, etc.
In the long run, IME, it tends to work itself out.
EDIT: I just realized a point system of
1- easy
2- moderate
4- hard
8- deadly
at 6-8 moderate/hard encounters would generate 21 points on average. So, one hard and two deadly encounters--which likely might require a short rest after each, would give you the attrition needed for an adventuring day most likely. I prefer to spread it out a bit more, but it might work...