An introduction to the Planes and the Multiverse

Before stepping through any door, a body'd better have a quick lesson in cosmology - how else is a basher going to know where and what things are? First, it's important to know just what a plane is. To the serious philosopher types, a plane's a world, or a collection of worlds, that operates according to its own particular laws, including those affecting magic, gravity, and even the morals of the place. On some of these planes, the laws of "up" and "down" aren't the same; on others, evocation magic yields different results; and elsewhere, behaving even slightly out of line with the powers of the place makes for grim results.
Planes are either immense and infinite, in which case they're just called planes, or they're limited by definite borders and are called demiplanes, The exact number of planes is unknown and probably infinite, and planar travelers know of only three main categories: the prime Material Plane, the inner Planes, and the Outer Planes. Still, those three have more than enough space for a flaming large number of different planes. To get around in the planar multiverse, there are three basic rules to remember:
  1. The Center of the Multiverse
  2. The Unity of Rings
  3. The Rule of Threes
These truths pretty well describe the structure of all the universes, so learn them well!

The Centre of the Multiverse
It's usually upsetting to Prime Material bashers when they hear that their little world isn't the center of the universe, which is why they're known to planars as the Clueless. Members of a faction
called the Signers might argue otherwise, but smart folks say there's no particular center to the planar multiverse. Rather, it all depends on where you stand. Folks in Sigil see the City of Doors as the center of the multiverse, folks on the Prime Material Plane say their own worlds are the center of the universe, and the Efreet brag that the City of Brass is the center of all. The thing is, maybe they're all right and maybe they're all wrong. Maybe they're all right because - the multiverse being infinite by most standards - no matter where you stand, that's the center of all things. The Signers have turned that idea into a whole philosophy: "I'm always at the center of the multiverse; therefore, I must be the center of all universes," they say. Of course, the Signer's aren't quite right, because by that logic everyone stands at the center of the multiverse. (The Signers resolve this little paradox by ignoring it.)
In blunt words, the fact is there ain't any place in the whole multiverse that's more important than any other. For instance, Toril on the Prime Material Plane is not the most powerful, influential, and important point in the multiverse; it's not the sole reason all other planes and powers exist. Hey, the uncounted layers of the Abyss stink of Evil itself, but exactly zero of the other Outer Planes kowtow to them, regardless of what the fiends there claim!
Some places - like Sigil - are more useful than others, though. Just because it's not the center of the universe, don't think it ain't important, berk.

The Unity of Rings
A ring's a thing without a beginning or end. Remember that, because rings are the second key to understanding the planes. Everything comes in rings. Sigil is a ring, the Outlands are many rings, the Outer Planes form a ring, the Elemental Planes form a ring - this is the way of the multiverse, understand?
On the Outer Planes, the Great Road is the band of the ring, and all the planes are its gemstones. Following the Great Road, Mechanus leads to Acheron, Acheron leads to Baator, Baator leads to Gehenna, and so on. By following the road, the order never changes. On the side, the powers think in rings, too - circles upon circles of logic that go nowhere. A body's always got to watch out for their endless snares.

The Rule of Threes
"Good things come in threes" they say. Well, so do bad things. Either way, the number 3's important - some say it's got power. Things out here tend to happen in threes, like Prime Material, Inner, and Outer Planes; Good, Evil, and Neutrality; Law, Chaos, and Neutrality; even prime, planar, and petitioner. See two things and ask. "Where's the third?"

Denizens of the Planes

A lot of sods from the Prime Material are amazed to see so many folks out here. Poor berks, they just haven't learned they're not the center of the universe. 'Course there's lots of folks on the planes, because this is their home! Everybody out here can be sorted into primes, planars, petitioners, proxies, and powers, and just who's who makes a big difference. It don't pay to confuse a planar with a petitioner, for one.

Primes
"Primes" is a polite way of naming them - more often they get called Outsiders or Clueless. Primes are mortal travelers horn on any world in the Prime Material Plane who have since ventured beyond their narrow realm. They're usually humans, elves, dwarves, and the like, but don't be too quick to label anybody as a prime or anything else. (Woe to the berk who calls a githzerai a prime!) Most primes are just visitors who journey to the planes for some particular purpose, but some are adventuresome types who've set up permanent shop on the planes, most often in Sigil. A few prime settlers are found scattered about the Outer Planes (mostly in the upper reaches), and wizard primes like to make demiplanes in the Ethereal, but neither's very common.
Primes got one big advantage over the local folks: They're not susceptible to planar-related magic . Seems that while planar folks are sensitive to spells that protect, summon, or banish, the primes are completely immune. A monster summoning will never drag primes away at an unexpected moment, and a holy word won't go casting them back to their prime-material world. Even a protection from evil spell doesn't consider them extraplanar creatures.
It pays to treat primes with respect, even if they've got a load of peculiar ideas. Getting to the planes takes power, and more than a few primes could boil a sod's blood just for looking at him sideways. 'Course, not every prime's powerful, but the problem is, with their funny habits, there's just no way to know. Remember, most primes don't know the lay of the land. They mostly think their tiny world is the center of the universe, and they've never heard of the Rule of Threes or the Unity of Rings, either. They're likely to think that just because a thing's got horns, it's evil. They can be easy conies for the bobbers, but real touchy if they learn they've been had, so be careful around a prime, at least until he shows you what he's got.

Planars
Most folks out here are planars, born and bred on the planes. Planars ain't all horrible monsters or whatnot; that's a mistake some green prime's likely to make. Planars include all sorts of folks: humans, halfelves, githzerai, and the like, in addition to some more exotic types. One thought worthy of a prime is that those same humans and half-elves can't be native to the Outer Planes. Some primes think their races are unique to the Prime Material Plane. Well, maybe that's where humans and halfelves first came from, but these people have been living in cities and towns out here for millennia. Way back at the Beginning, humans were probably unknown out here, but with time the lost, the curious, the exiled, and the just blamed unlucky made themselves homes out here on the planes.
On the surface, it should be real easy to tell a prime from a planar, but it ain't. A human - prime or planar - looks like a human. A body's got to talk to them and know them to be sure what they are, which is another good reason to treat them all with respect. With others it's pretty easy to tell; a githzerai, bariaur, or tiefling's pretty easy to peg (but it pays to be respectful to them, too).
Planars do have powers that make them different from primes. It's part of their extradimensional blood, something that just comes from being born a part of the extended cosmos. Planars don't have a silver cord, that magical thread that ties a prime back to his or her prime-material world. Planars also have the power to see the gates between planes. ('Course, these crossing points are limited to certain locations. A planar can't just will himself onto the astral anywhere. He's got to journey to wherever the gate is.) Those mesh the planes are clear to any planar. A prime won't see anything, but the glowing outline of a portal.
Planars got their weaknesses too. That are, in fact, extraplanar and suffer from things like protection from evil, holy word and exaction.
Almost as bad, planars can be hauled off to the Prime without notice by monster summonings and the like.

Petitioners
The majority of bodies on the planes are petitioners, which are departed spirits of primes and planars whose bodies reformed on the plane that matches their previous alignment or devotion. A petitioner retains the mannerisms, speech, even general interests of his or her former self, but all memories of the past are wiped completely away. At best, a petitioner has a , shadowy recollection of a previous life, but little or nothing useful can be learned from these fleeting images. Petitioners mostly desire to attain some ultimate union with the powers of their plane. This can be accomplished in a number of ways: good works, serene contemplation, steadfast faith, or vile notoriety, depending
upon the petitioner's alignment.
Petitioners hate leaving their home plane, as "death" outside that place results in oblivion. Fact is, they can't be resurrected if slain at home, either; once dead, the petitioners' essences are merged with the plane, but they figure that's better than nonexistence. Still, a power's got to raise an army now and then, and it may be petitioners that fill out the ranks, but that's the only way they'll ever leave their home turf - on the boss's orders. Petitioners tend to view all things as a test of character. They ain't eager to die, but they'll take that risk in order to further their own goals. For example, a petitioner warrior on Ysgard will fearlessly rush into baffle, since combat is the glorious and right thing for him to do.
Petitioners are never player characters, but they often appear as 0- or 1st-level nonplayer characters. They can't gain additional levels or abilities unless elevated to the station of proxy. In a planescape campaign, petitioners fill the roles played by commoners in prime material worlds: landlords, grooms, spies, farmers, guards, etc. Petitioners aren't identical to commoners, though, for they always have a greater goal in mind (i.e., to merge with the plane on which they reside).

Proxies
Some Outsiders think every planar's a proxy, but that just ain't true. Proxies are those beings - primes, planars, and even petitioners - specially chosen to act as agents of the powers. Usually, the body chosen is transformed into a creature favored by the deity - into an evil rutterkin or a good deva, for example. On rare occasions, the being isn't transformed, but is bestowed with special powers. Proxies are absolute servants, obeying the wishes of their deity as fully as is appropriate to that alignment. Those of good powers are unswervingly loyal and obedient, and those of evil powers are utterly difficult and tricky, even for their masters. On the Upper Planes, a proxy knows he can rise even higher through good service. On the Lower Planes, a proxy usually prospers by finding some clever and nasty way to create an opening for his high-up man.
Proxies are never player characters unless a power intentionally makes them one. Normally they are elite nonplayer characters who serve the powers. Their abilities are specifically granted by the deity who makes them a proxy, so their skills will vary according to the scope of their assignment. Proxies may join the playercharacter party for a short while, or they may oppose it.

Powers
Finally, there's the powers. Make that Powers: the deities that preside over the planes. Now, the Athar claim there just ain't no gods, but it don't matter if they're right or wrong because the powers definitely exist. Once more, they've got more might in their thumbs (those that have thumbs, that is) than any mortal's ever going to have, so be careful what you call them, berk, as the powers can have mean tempers. They can turn a man inside out and leave him still alive, or drop him off in the deepest layer of the Abyss with only half a map.
Actually, the powers don't take as much interest in the goings-on of the Outer Planes as they do in the Prime Material (excepting the Blood Wamors). It seems they get their strength mainly from the worlds on that plane, sucking up energy from their worshipers there. Without this energy they'll die - as much as an immortal can die. Getting a god killed ain't easy, though, since first there couldn't be a single worshiper left on a single prime-material world. (Not a simple task, eh?) Long before it dies, a power weakens to the point where its body is cast out of the Outer Planes to drift in the Astral Plane. It might cling to life forever or it might fall into an immortal decay - and depart for the realm of some ultimate god. That's not a fate most powers look forward to or allow, if they can help it. (Of course, they're used to being the biggest fish in the sea, so who can blame them?)
It's not that the powers ignore their worshipers on the Outer Planes. A deity's got to protect itself from the dealings of its fellows, so its plane-wandering clerics also get spells and granted powers, and they may even get called to help with a special mission. It's supposed to be a great honor to get chosen for a quick raid on baator, just to recover a flower or whatever nonsense is required. Still, there's a bigger price for saying "No" so it's an honor most priests don't refuse.