Gods & Goddesses

In Rydoneus it is said, "As long as someone believes in them, they're bound to exist somewhere."

Religious Worshippers
There are other gods that exist in Rydoneus that do not have months or days named after them. For example one paladin organisation worships Heironeous, the god of chivalry and valor.

Other species like the Kuo-toa will simply make up gods or worship whatever they seem fit. This has lead to gods being summoned into existence that were previously unheard of. On tribe of Kuo-toa (that no longer exist) brought back an ancient demigod that struck down wrath in Gezmadon, but now that the tribe is gone, he ceases to exist again.