After millennia of no divine contact, deities were able to reconnect with the peoples of Skarr. Due to the nature of Skarr being the destination for many campaign worlds, serious consideration is needed to determine how to treat deities in this new paradigm.
Each domain (War, Sun, Healing, Death, etc) is controlled by one or more deities traditionally. Sometime this is a collaboration, and sometimes it is a competition. After the cataclysm, a secret about the nature of deities was revealed – they are indeed very powerful, but not omnipotent. The same group deities exist in all worlds. The same small group of entities take on different, albeit similar roles from one world to another. For instance, one entity is consistently associated with the power of the Sun, and different cultures name this entity Ra, Apollo, Helios, Sol, Surya, Pelor, Aurifar, etc. These entities play their god games, where each civilization and culture is a different chessboard. They vie for power, mortal enemies in one culture, while companion but opposite brothers in another. Although the rules are not understood by mortals, we now know that there are a few deities all wearing multiple masks, for their own mysterious purposes. As this knowledge became more well known, the gods and temples tend to be more accepting of those who worship their god “by another name”.
This allows followers of Pelor the sun god (previously from a Greyhawk campaign) to freely worship and regain divine spells when praying at a temple of Ra, or Apollo, etc.
Another interesting point about gods is when they can physically manifest in this world. When a high priest of a certain religion (pure cleric, no other levels of at least 18th level) is touching a 9th-level temple altar, the high priest may offer up his mortal body as a vessel for his god to inhabit. Normally, this is only done at the bidding of a god. For a short time, the god may invest a large amount of it’s power in the body of the high priest, essentially using it as a vehicle for it’s divine purposes. This does, however, destroy the high priests mortal form. Since gods are reluctant to destroy their most powerful followers, as well as spend vast amounts of accumulated power, this event may happen one or twice a century across the multitude of worlds, and is always an event carried through the ages into legend forever after.