Planes of Power
Setting Variant Rules
Magic isn’t always so magical in the planes. In fact, it can be a pain in the ass since magical effects can change from plane to plane. Some effects are enhanced in certain places and diminished in others. Some do not function at all based on where you are.
Additionally, magical weapons are most potent on their plane of creation. The further from its plane, the less magical it is. A +2 Longsword (Abyss) functions as a +1 Longsword on all planes it is adjacent to and a +0 Longsword on all planes it is separated from by more than 1 plane. A weapon never becomes a negative, and a magical weapon still qualifies as a magical weapon for overcoming resistance that requires magic. Magical armor functions the same way. Obviously, some planes are better than others for producing weapons & armor. The Outlands touches all Outer Planes. The Astral plane also touches the first layer of each of the Outer planes. Weapons from these places tend to be more valuable.
It is worth noting that magical weapons with special properties can temporarily lose those properties as well. (A “Weapon of the Planes” is one of the few exceptions to this, but these coveted weapons are extremely rare and well-guarded. People commit heinous acts to get these. Similarly, the Holy Avenger typically retains its abilities in all the Outer Planes.)
The function of magic items other than weapons & armor may also be affected. The Planes Cosmology skill is very useful in answering questions about what will work & where, although in some cases Arcana may also be used.
I will add one last note: it is possible to find “archaic” magic items, i.e. ones which function similar to items from previous editions. When I add these, I try to update the rules functionality while preserving the archaic feel. If one of them turns out to be broken, I will apologize and make changes to it.
Arcane Magic & Spell Keys
Similar to magical items, arcane spell effects shift from plane to plane. A spell can be diminished, enhanced, nullified, or altered. When casting a spell, you may be asked to roll a spell skill check. (This roll is a spell attack roll against a DC set by the plane itself.) Failure may cause the spell to be diminished (in any of damage, efficacy, duration, number of targets, etc.), nullified (spell completely fails), spell is altered (any of different effect, duration, targets, etc.). In some cases, the check is to see if the spell is enhanced. In that case, failure has no effect; but success can enhance any quality of the spell or even cause the spell slot to remain even after being used.
There is a way to keep your spells functioning at peak efficiency. Arcane casters can use spell keys. The original 2nd edition setting was specific about spell keys; I am going to be more vague (this is to your benefit.) A single spell key covers all the spells of one school and level, and it allows those spells to function normally on one plane. Basically, a spell key equates to an automatic success when a spell skill check is required.
You know a number of spell keys based on the chart below. The Arcana and Planes Cosmology skills are important here. (See Character Creation for information on the Planar Cosmology skill.)
During creation, arcane casters should decide which spell keys they know. For example, if you had 3 spell keys, you could pick “Necromancy1-Abyss” as 1 spell key; this would cover all 1st level Necromancy spells when cast in the Abyss.
If you want more spell keys than are present on the chart, you can always use a skill or tool proficiency to gain more. Doing so gives you a number of keys equal to your proficiency bonus (which means gaining levels automatically gives you more).
Sometimes a spell needs more than a general spell key. Fear spells tend to not work on Mount Celestia, the home of paladins and their ilk. But there just might be a specific spell key that allows that spell to function there. These spell keys can be learned through role-playing in the campaign. They do not ever count against the number you know (based on your ranks.)
Some hints… spell keys can change over time (especially in Limbo). Hint #2: sometimes a spell key does not exist. The current chant is that there is no spell key which will make a fire spell work on the elemental plane of water. Hint #3: some planes, like the Positive & Negative Energy planes enhance some specific spells without a spell key.
The Divine is Near
Well, it’s near MOST of the time. Since the Outer planes are the homes of the powers, divine spellcasters drawing spells from particular deities have a problem to contend with: there is more than one power out there, and most of them don’t like interlopers.
What’s this mean? In mechanical terms, when casting or channeling divine energy, your ability to draw divine energy decreases. Sages refer to this as “Divine Drain”. The Drain is equal to the number of planes between you and your power. On the Outer Planes, you go around the ring, not through the Outlands when calculating. The Drain is temporary and only affects spells and Channel Divinity; it does not affect other divinely inspired gifts. There are two places where there is NEVER any Drain: Prime material plane and Sigil.
It is important to note that you do not lose spells or access to spells. Instead, your spell attack rolls and DCs decrease by the distance to your deity’s home plane. The good news here is that you cannot lose more than your proficiency bonus.
Oddly enough, Paladins suffer Drain with regard to spellcasting and Channel Divinity, but not on any of their other abilities. Theories as to why have abounded for centuries, yet no certain answer as to how & why is to be had. Rangers & Druids tend to not see Drain (although the nature of some planes is definitely NOT friendly to them.)
Of course, I should not forget to mention the way around these effects… Power Keys. A Power Key is a gift from one’s deity. Based on the strength of the power key, they can have multiple effects: decrease or remove Drain, allow the function of a single spell, group of spells, school of spells anywhere in the multiverse, maximize a spell effect, etc. Divine casters do NOT automatically get these the way arcane casters do. Sorry. As they are a small portable portion of the deity’s power, they must be earned.
The Mind is Strong
Psionics, like arcane magic, is affected by the nature of the plane it is on. Like arcane magic, a power can be diminished, enhanced, nullified, or altered. When manifesting a power, you may be asked to roll a Manifester skill check. (This is rolled the same way an arcane caster rolls; see above.) Failure may cause the power to be affected the same way arcane magic is. Unlike arcane magic, psionic keys do not exist. Why would they, after all, since the power of the mind does not draw upon outside sources for strength?
That said, many psions have found that certain kinds of crystals can assist them with their focus. If a psion can find the correct psicrystal, they have advantage on the Manifester skill check. That is the easy part. Unfortunately, psicrystals are very rare, and the secrets of using are not well-known at all. If you play a psion, it will take trial and error to learn which crystals are psicrystals and which psicrystals can help you manifest on different planes. (In other words, you have to find and learn these through roleplay.)
Throughout Sigil, and in many other odd places, portals connect the various planes and layers. Many of these require a Gate Key – a substance, action, thought, etc. that allows the gate to function. Thus, a portal can be a door people use daily, but without the key, it is a door, not a portal. Gate keys are often for sale in Sigil, as is the knowledge of portal locations, etc. Knowing there is a portal to Bytopia and getting there are not equally easy. Gate Keys can change, as can the location of portals.
There is a wide variety of portals. Some are two-way, some are one way, and others are paired (2 different outbound locations, 2 different inbound locations, but the same key for the same plane), and some are just odd (one portal is the outbound doorway to one place but the inbound portal from a different spot on the same plane). There are people in the Cage who make their entire living by knowing of portals, while others make a living selling gate keys for various portals.
Magical Item Purchase
Obviously, Planescape is a high magic setting. Due to the nature of the planes, buying or selling magical items is not exactly easy; after all, the value of a thing changes based on where the item was created and where it is being sold.
That said, the prices in the DMG are – at best – very loose guidelines. I do not feel beholden to use them.