Kemrain said:
Has anyone discussed the ramifications of this? Could a Faerunian cleric cast spells in Greyhawk? How do the Gods react to creatures from beyond their realm?
This was well-trod ground of rules and setting before 3rd Edition (which kinda ditched the whole concept and doesn't really acknowledge worlds co-existing), and was integral to Planescape and Spelljammer (maligned though it may be, it still used the same basic rules as every other AD&D book on the subject), and it was covered in the 1e Manual of the Planes. To restate the basic concepts of what came before:
Any divine spellcaster can prepare and cast 1st and 2nd level spells, even if they can't access their god in any way, shape or form, or even if their god is dead. 1st and 2nd Level spells come from a combination of training, experience, and the personal faith of the caster.
3rd and 4th level spells can be granted by outsiders affiliated with a divine being, acting as agents of their deity or middlemen distributing divine power.
5th level and higher spells require the actual intervention of a deity to grant. Earlier editions had rules saying that only certain power levels of deitys could grant certain spells (i.e. if you worshiped a demigod, you'd never get higher than 5th level spells, and you'd have to pray to an Intermediate god to get 7th level spells, which was as big as they got back then). 3rd edition seems to have completely ditched this, and the idea I don't think would work right with standard 3rd Edition.
If a divine spellcaster goes to a world where his deity does not have access, he has the spells he has prepared at that time, and that's it. When he regains spells, he can only refresh spells of 1st and 2nd level. If an extended stay is planned, a divine arrangement may be arranged to gain spells through a similar deity, presuming those deities are on friendly terms. A cleric from Oerth who prays to Pelor and ends up on Toril and finds himself stuck there for a while may find that his appeals to Pelor are quietly being granted by Lathander (and that somewhere in the Outer Planes, Pelor and Lathander have agreed to this arrangement, presumably in exchange for a favor or reciprocal treatment for any Lathanderans that visit Oerth).
If a cleric of a deity that doesn't have access to a world tries to recruit and expand his faith, several things can happen, and bringing a new god in isn't easy or guaranteed even under the best of circumstances.
First, he has to get an actual following of that deity going, with people praying to that deity for intervention or action. Since their priests won't be able to cast spells above 2nd level, this can be hard. However, when a significant number of followers are in existence (the exact number is never certain, it's DM's discretion, but a few devoted congregations or a widespread but not overly devout following could should do it), then the deity can attempt to access the world (crystal sphere).
Once this happens, the locals get their say. First, the deities of that world may object, and assuming they haven't already been warring on the new faith, they might start now, if it's a big enough issue, deities might even war in their Planes if they object to it strongly enough, but this is unlikely. If the deities don't manage to either crush the new faith or destroy the new god, the Overpower of that world gets his say.
I don't think the Overpower of Oerth has ever come up, but in Abeir-Toril and Krynn and presumably other prime worlds, a single overdeity has final, controlling power over what deities can access the world. Normally occupied with a concept of divine balance or some other concept of ensuring the continuity of their own world, if they approve, then the deity can access the world, grant spells normally, and is a permanent member of the pantheon (in the Realms, this is how the Mulhorandi gods arrived, when slaves brought in from other planes prayed to their gods for intervention and Ao let the pantheon access the world).
As was said,
On Hallowed Ground was the best work on the subject, one of the best D&D books on gods ever, definitely the best from a planar/multiworld perspective. It was
the book of Gods for Planescape, and included in it a comprehensive directory of every god for every D&D world ever published (and a large number of real-world pantheons too), with name, alignment, power classification (Lesser, greater ect.), and portfolio. You can probably find it for download, or search eBay. Physical copies of it are relatively pricey compared to other 2e books in my experience, because it is relatively rare and is in high demand.
