I'm going to open with a hot take - I don't think it's intrinsically bad to set a campaign in a universe with no breathable air where the environment is constantly trying to kill you.
That's what people say, isn't it? That inner-planes adventures are pointless because in almost all of them (with the plane of Air being the one possible exception) it is impossible for mortal creatures to exist without the aid of magic. And, indeed, when you read about, say, the quasielemental plane of Dust, and the text itself says, "what sane person seeks out a land where ultimate disintegration is the only sure fate," maybe that does feel a little like the game begging you not to play it.
However, when I think about hostile environments that inevitably lead to a quick and painful death for the unprotected, I can't help thinking about outer space. Outer space is just as dangerous as the inner planes (maybe even moreso, the plane of Vacuum "is marked by the complete lack of air, [but] there is still pressure and constant temperature"), but it is at the heart of entire genres of stories.
So why not a fantasy version of that? Why say that outer space is cool, but the inner planes are pointless? I think what it comes down to is how the methods of survival help to define the setting. In science fiction, the architecture and engineering goes a long way towards building a genre. If you're in one of tiny orbital tin cans of hard SF, constantly oppressed by the closeness of the void, that says something very different than crystal domes on the moon and personal environmental forcefields. There's a problem, yes, but that problem is an opportunity for you to explore how the problem is solved.
The inner planes could be the same way. They aren't, at least not if The Inner Planes is taken to be the definitive word on the subject, but they could be. What it really comes down to is the blandness of AD&D's magic system. How it works is that you have a problem and then you cast a spell to solve the problem, but the way spells solve problems is by just . . . working. Cast "Water Breathing" and you can breathe underwater. Need to breathe in the thin, dust-choked atmosphere of the Quasielemental Plane of Dust? Cast "Breath Smoke, Dust, and Ash" instead. There's no specificity here, no sense that you are overcoming an obstacle by exploiting an understanding of cause and effect.
For instance, rather than give a character a cloak that protects him from all fire and heat, the DM could create a cloak of elemental magma survival. With this item, the wearer would be able to survive in the Paraelemental Plane of Magma, but he'd still be vulnerable to fireballs, red dragon breath, and even magma paraelementals. Likewise, a ring of elemental earth travel might let a cutter move through the substance of the plane of Earth, but not through normal stone in any other plane. Thus, special items provide the opportunity to adventure in the Inner Planes without giving the PCs too much magical power.Ah, of course, the "Ring of Surviving in the Setting of the Adventure," why didn't I think of that? Such an elegant solution.
Like, maybe this is just me pitching oddball ideas here, but you've got a need for mortal colonies in the world where everything is constantly on fire and you've got the rare treasure of Eternal Ice, which always stays cold and never melts under any circumstances. Maybe those things might have some connection. Then you could work out the logistics of how the ice is used to cool human settlements, and there could be a trade route by which the ice is transported to where it's needed, and maybe the natives aren't happy about that and by exploring the economic and political implications of your technological solution, you could do some complex and engaging worldbuilding that leads to a whole campaign's worth of adventures.
Or, you know, whatever.
I do have to rein in my cattiness here. The Inner Planes has a lot of good fantasy ideas. The City of Brass is an iconic location. The plane of Water has thousand foot long sharks. The plane of Ooze has overly friendly animentals (elemental animals) - "There are few things as revolting as having an ooze cat hop into a sod's lap or a slime dog lick her face." (Speak for yourself! I guarantee 90% of the time that's going to be the highlight of the campaign). The writers, Monte Cook and William W Connors, were good at their jobs, but I'm not sure they understood the assignment.
Or, maybe, whoever gave them the assignment didn't understand the assignment. It's hard to say. The Inner Planes is probably the most methodically-paced rpg book I've ever read. The four main elemental planes get 10 pages each. The paraelemental planes get 6 pages each. And everything else gets 4 pages each. Often, in an rpg supplement that has to share space between subjects, the division won't be nearly so clean. The more interesting subject usually eats a couple of pages from the less interesting ones (for example, in The Factol's Manifesto, the Harmonium gets 12 pages and the Transcendent Order gets 8). But that doesn't happen here. The plane of Ash starts developing a plot about the legacy of Vecna and the ambitions of the Doomguard remnants (it's a whole thing that we're going to have to talk about later), but it reaches page 4 and cuts off. Whereas with the plane of Vacuum, it goes all the way to page 4, even though half its word-count is "no, really, we mean there's nothing here." Towards the end, I got the feeling that most of these chapters were being written up to meet the page count, rather than being edited down to fit in the space allotted.
It's this lack of conviction that is the book's ultimate undoing. You get 4 pages to describe the quasi-elemental plane of Lightning, then what I want to hear is a condensed version of Storm World, the 250 page core book that spawned its own line of supplements, set in an archipelago of floating islands, with cities protected by rings of lightning rods, which harness electric power to drive advanced industry and magical research. Where transport is via airships fitted with lightning impeller drives that catch the bolts of lightning and ride them at 20,000 miles per hour. Where gods and heroes wield the thunder and where ancient treasures lie in the great ring of storms that surrounds the habitable lands. You know, the setting that people are excited about, and which could support any number of epic campaigns.
Instead, we get, "the vast majority of the quasiplane is little more than one storm-cloud after another. A few areas, however, stand out as curiosities." We learn that "the mephits have no doubts that something or someone lives in the tower [of Storms]." Dude, "something or someone?" That's what you're going with, in the one and only spotlight this mysterious tower, which was teased in the original boxed set, is ever going to get? Am I even meant to be playing this? Who is it for?
Planescape challenges me because it's clearly a labor of love, and a chance for TSR to stretch its creative muscles, but also so much of it seems half-baked. Maybe it's a side effect of making 30 books in 4 years. You're passionate, sure, but you've got a month and a half turnaround time so you stick to the template. Getting Here. Hazards. Moving About. Quasielementals. Animals and Monsters. Major Players. The Sites. Planeswalkers. One down, seventeen more to go. Repeat. If you've only got a day to work on each plane, maybe you don't want to pitch anything that's going to take more than a day to develop. Sticking to the pattern would definitely help.
Although, I wonder if maybe the composite nature of Planescape might have something to do with it. So much of the setting is inherited from the rough sketch at the end of the Player's Handbook and it mostly has to stay canon. There's a plane of Ooze and there's nothing anyone can do about it, and so you just try to get through the six pages with dignity. Yet Planescape also has a lot of innovation. Sigil, the factions, tieflings and aasimar and genasi, most of the Outlands. Things that are voluntary in a way the planar checklist is not. Maybe that's why the Sigil books feel so original and this one feels so obligatory - because that's exactly what they were.
It's certainly a theory, though I'd be remiss if I didn't post the counter-evidence. That stuff with the Doomguard I alluded to earlier - it's a spoiler for the Faction War adventure. Here's what we know from the description of the Crumbling Citadel: There was a big war in Sigil. The Armory was destroyed in the fighting. "The Lady of Pain outlawed all the factions." And, I guess, we can infer that the Doomguard's four quasielemental citadels were divided up between different cliques inside the faction, because each of the different citadels gets a different attitude towards the inevitable decay of the universe.
I guess I kind of assumed my historical distance would inure me to these kind of metaplot blindsides, but what?! Outlawed the factions? What does that even mean? How is Sigil being governed? Why would you blow up the setting so close to the end of the line and then publish books set after the big event? Ending the series with a big even makes sense, but did you think Planescape had another couple of years left in it and that's why you wrote the last three setting books post-Faction War? If it was a marketing scheme, I guess it worked, because I'm just going to tab over to ebay and . . .380 dollars?! . . . ::choke:: ::gasp:: . . . um, let this remain a mystery for now (yes, I know I could get the pdf, but I'm holding out for a PoD).
Still, it pokes a hole in my theory that the Sigil stuff was the passion-project aspect of Planescape. So I don't know what's going on here. I guess maybe the para- and quasi- elemental planes are kind of an afterthought and this is just a relentlessly checklist-driven book. It has its moments of inspiration, but it probably would have been better if it had just covered the four big elemental planes and left the others as locales inside their nearest counterpart. Thirty pages per plane would have made the workhorse parts of each chapter ("here's how much damage you take just from existing in this location") into a lot smaller percentage of the wordcount, and given the good parts of the planes - the creatures, locations, and treasures - much more room to breathe.
Overall, I'd say that this book is . . . okay. For almost anywhere in the Inner Planes where you might want to set a game, you'll have to write almost the whole thing by yourself, because it frequently confuses the concepts of "there is no large body of canon lore yet" and "there is nothing significant to know about the place." It keeps saying that there's only one "major player" in each of these lesser planes, but that is clearly only the case because the chapter is running out of pages. The Plane of Steam is infinite, so how can the only being of significance be the silly-talking Slaad who narrated the chapter? Why not the rival gangs of tinker gnomes who power fabulous war machines with the plane's infinite energy and make them fight each other in ever more devastating spectacles, oblivious to the fact that fiendish infiltrators are busy taking notes?
Sorry, I drifted into brainstorming mode there. That's kind of best use of this book, though. You're going to do most of the work yourself, but the 4-10 pages might serve as inspiration, and the frequent, if fleeting good stuff can make a cameo.
Ukss Contribution: This is a tough one. There are a lot of candidates. Brine Dragons. The Fields of Nevermore, a region in the Plane of Magma where a cursed chillsword has frozen the plane into rock, creating a habitable bubble. Giant icebergs floating through lightning storms, appearing to glow from within. Beacon Seeds, that lead you back to their parent plant when you swallow them.
But, of course, it's got to be ooze kitty. Normal cats are already about 20% ooze. Going the rest of the way gives you dangerously high levels of party mascot potential. Ah, let's do slime dogs too. When the bait's this obvious, you've got to snap it up.