Here's an example of what I'm talking about, so people have a better understanding of what I mean:
Since the group was just on Carceri (the last adventure), here would be the magical conditions for that plane:
- Conjuration: A berk performing summonings on Carceri is likely to ge a nasty surprise. Though the summoning still brings the called creature to the caster, the creature isn't bound by the spell. Summoned creatures aren't specifically hostile to the caster (please note that the intelligent ones almost always will be), but the caster has to give 'em some show of good faith, offering a bribe to make them want to work for the caster. Otherwise, they turn on him and tear him to pieces.
- Divination: Carceri is indeed the plane of treachery and back-stabbing; any divination spell requires the sacrifice of a comrade. The spell takes shape in the spreading pool of the poor sod's blood. It's for this reason that diviners are universally hated on Carceri-- and bonds of treacherous friendship form between those who practice the forbidden art.
- Necromancy: Healing spells function at half their normal power on Carceri; nothing about the plane is conducive to life-giving powers. Spells that create undead or cause damage, on the other hand, are much more efficacious. Raised undead are automatically free-willed, and may well choose to attack the caster, while damage-causing spells grant a bonus of +1 per level of the caster to the damage caused.
- Transmutation: Spells of this achool always turn to the most evil result possible. If the spell can't actually produce evil, it manifests itself in a hostile way; flames writhe into tortured faces, while sigils and symbols twist around into horribly screaming faces.
Spell keys allow a spellcaster to bypass some of the above restrictions. They enable casters to cast spells so they function normally on planes where such magic is altered or even completely ineffective. Some keys prove more useful than others to a spellslinger. General keys allow a cutter to effectively cast any spell from a group of spells (such as all Transmutation spells), while specific spell keys only affect one particular spell (such as the
invisibility spell on Arcadia). Regardless, spell keys are particular to the plane they're intended for, and won't work on other planes (and in a few rare cases, there is no spell key for that plane). Be warned that on some of the more chaotic planes, spell keys can shift unexpectedly; what might work yesterday might not work tomorrow.
Spell keys for Carceri would have been: The conjuration key is a perfectly round, fist-sized lodestone. For divinations, the key's a good quantity of the caster's own blood-- not comfortable, but preferable (to most) over sacrificing a companion. The necromancy key requires the thigh bone of a farastu gehreleth. The transmutation key is a lead necklace, worned wrapped around the wrist of the caster.
They're not big mysteries and most of them can be found with a modicum of research or decent ranks in Knowledge: Planar (except for the shifting keys-- you're better off asking the natives or a lanned blood in that case).
Hey, if you guys think this is too much of a problem, we can ditch it. But I thought it would add a lot of flavor to the setting and had been sorry to see it go in 3e.