Consistency

This article, Under the Hood of the DMG, has a paragraph in one section that stirred up some strong responses, and in my opinion, is one of the markers that demonstrates part of the schism with Old School style play. Here is the passage:

The shift in philosophy reflected in this table is most evident in the section on terrain in Chapter 4 (pages 67-68). In past editions, we'd describe things like cave slime as if the DC of the Acrobatics check to avoid slipping in it were an objective, scientific measurement of its physical properties. "How slippery is cave slime? It's DC 30 slippery." But setting a fixed number like that limits its usefulness -- cave slime would be too challenging for low-level characters and irrelevant for high-level characters. In 4th Edition, we tell you to set the DC to avoid slipping based on the level of the characters, using the Difficulty Class and Damage by Level table. So when 5th-level characters encounter cave slime, they'll be making a check against DC 22, but 25th-level characters have to make a DC 33 check.

Does that mean that high-level characters encounter Epic Cave Slime that's objectively slipperier than the Heroic Cave Slime they encountered in their early careers? Maybe. It doesn't matter. What matters is that the DM has permission to use terrain that's relevant to the characters, regardless of their level -- and has a table supported by solid math to make sure it's relevant.

(A quick comment about the math: it may sound unfair, but with the independant mathematical demonstration that the Skill Challenge system is almost precisely the opposite of what was intended cropping up no more than a week after the books hit the shelves, I take the notion that other mechanics dealing with skills and such have "a table supported by solid math to make sure it's relevant" with a hefty bit of salt. Not that skill use is utterly discredited, but certainly, claims to the validity of the math have to be compared to that.)

The idea is that consistency should take a back seat, or not be in the car at all, really. I am also baffled by the bit where this is intended to give the DM permission, essentially, to challenge the players. If there was an additional explanation that the DM should challenge the players rather than thwart them, that would be different. But the underlying assumption is that the DM would simply sit passively while the players told their own story without intervention.

At any rate, the real implication was that the particular cave slime didn't have a DC for crossing it until the characters encountered it, then it was a DC that was appropriately challenging. In the barest terms, that means it would be DC15 or so at 5th level, but DC 40 at 25th level (just to throw some numbers out there). This is entirely contrary to how a consistent world works. In fact, as evidenced by the statement "...as if the DC of the Acrobatics check to avoid slipping in it were an objective, scientific measurement of its physical properties" shows a rather shocking lack of understanding. Of course you can measure the physical properties of the friction. It's called 'co-efficient of friction'. Naturally, an RPG doesn't require nearly this level of math to simulate walking on slime. But setting a DC for a Dexterity or Acrobatics check approximates it nicely. You don't even really need to get extensive research on microbiological algae papers and cross reference them with a materials science text. Calling it 'DC20' is more than sufficient to demonstrate that it is pretty slippery, and low level characters will have a problem crossing it intact. But, that is exactly as it should be. Likely, low level characters won't even be looking for slippery rocks that an experienced spelunker would see coming three passages away. As the caver gets more experienced in dealing with subterranean hazards (buys ranks in Knowledge:Dungeoneering) or the character gets a better feel for their surroundings and how to interact with them (buys ranks in Balance), then of course they will become better at navigating treacherous passages. Being able to surpass previous challenges, and eventually being able to surpass them easily is the very definition of improvement. Setting all and sundry challenges equivalent to the character's levels undermines the very idea of improvement.

In other words, James Wyatt is suggesting a sliding scale dependent on when the characters encounter a patch of cave slime. By implying that the same cave slime would have a different DC if the characters were to go back at a later level, the cave slime is removed as a part of the physical world the in which the characters adventure; it's a challenge based on the needs of the story at the moment. Now, some may wonder why players would want to go back to an area they have already 'cleared'. One reason is that some new threat has taken up residence. The same area and its secrets that were protected by cave slime earlier is probably still an excellent location for the secret plans, the lich's phylactery, a portal to another dimension, or whatever else. It really wouldn't make sense for the cave slime itself to have leveled up with the characters. But this is exactly what is being suggested. If that area still needs to be challenging to enter, then the previous DC20 cave slime should be DC40, so the higher level characters will be challenged.

Some prefer this, others don't. There is a kernel of good adventure design in there, but taken to the logical extreme implied by the article, you end up with a more or less generic ~50% of success at any level for any 'challenge'. Similarly, it makes the description rather pointless. It can be DC 40 cave slime, troll droppings, loose rock or tangle vines. Additionally, it makes consistency harder to establish. Certainly, there can be varying degrees of cave slime frictionlessness, but for the most part, keeping that to a certain number then adding other penalties makes for a consistent experience for the players. Cave slime covered in troll droppings, for example, should be harder to cross that either of them alone. If you simply put a 'difficult terrain DC40' in some area, the players won't know if it is easy to cross after gaining 10 levels, like DC15 cave slime, or if it was impossible to cross earlier, but may be reasonable to try now, like DC25 troll droppings.

Rather than

P1: "Should we try to cross it? It was a pain in the ass when we were in the Caves of Desolation"
P2: "Yeah, that was a long time/ten levels ago. We can make it, easy-peasy."
DM: "You notice there are also extensive troll droppings on the rocks, making them appear more treacherous."
P2: "Yikes! This might be trickier than I thought, troll droppings will up the DC by quite a bit"

You get:

P1: "Should we try to cross it? It was a pain in the ass when we were in the Caves of Desolation"
P2: "I dunno, what's the DC?"
or
P2: "Yeah, we got about a 50% chance, same as the Caves of Desolation 10 levels ago"

In the first case, a consistent DC doesn't prevent meta-game discussion or planning, and in fact, isn't really intended to. But it can keep it more to the background, as the players would probably know the DC of cave slime at least, if not troll droppings. They wouldn't need to check with the DM for a DC necessarily, and should be able to estimate the odds of making it across safely and base decisions on that.

In the second case, the only way to really navigate the hazard is by meta-game planning. It can be masked, of course, but in the end, they players have a good idea that the DM will be setting level appropriate challeges before them. So, no matter what kind of hazard they face, they will have somewhere in the 45-55% range to overcome it, no matter what level they are. "Always fighting orcs" as someone put it.

To a degree, the first case goes to the heart of Old School gaming. There is a great big world out there, waiting for the character's to interact with it. But it is a great big world, full of people with their own agendas, plans and desires. Some of them have been gone for years or even centuries, but their devious traps and carefully laid plans are still in motion. If the characters are low level, they will be tangling with things they are incapable of overcoming, to their detriment. An example: the 20th level necromancer may have been defeated 200 years ago, destroying the adventurers sent for that purpose. But not before ensorcelling the Book of Doom that will raise wave upon wave of undead to sweep the known world clean of any living beings, using the most cunning traps, calling upon the mightiest of dweomers, insuring that any but the strongest mage will be utterly rendered if they try to wrest the book from its unholy crypt. Not something you would contemplate at 5th level unless the situation is dire, indeed. Insuring this adventure is appropriate to the characters is a matter of campaign design, not sliding the DCs on the traps and such around for a party of 7th-10th level. Consistency is severely damaged, and the idea of adventuring in a 'real' world is similarly compromised.

Sliding DCs have the veneer of making the narrative more important, but even that is undercut by having roughly the same chance of suceeding at any level. An ever increasing list of adjectives may sound good the first couple of times, but it does nothing to emphasize character improvement when the odds don't change. If you have even odds to kick down a simple wooden door at 1st level, and even odds to kick down the adamantium bound soulsteel magical demon-gate at 30th level, what has really been accomplished, aside from increasing the numbers?