From the very first, The Kynthiad was never intended to be exclusively derived from Greek mythology, though that would be the primary source. The Bronze Age Near East was chock full of competing cultures and religions, such as Egypt, Canaan, and the Hittites, and it would be unrealistic to ignore them all. (I realize that "unrealistic" is a slippery word when you're talking about a fantasy setting featuring monsters, gods, and magic. I simply mean that Greece did not exist in a bubble.) My research also suggested that the most likely dates for the historical basis of the Trojan War and the Hebrew Exodus roughly coincided with the long reign of Ramesses II. Or close enough to make for a very interesting background to the game, without resorting to the violent mashing of timelines that, say, Xena: Warrior Princess regularly indulged in.
One of the first issues I had to address was how many of those other cultures, and their pantheons, to include in the game. To start with, Egypt was irresistible--it seemed as old and exotic to the "heroic age" Greeks as it does to us now. The Hellenistic Greeks' attempts to syncretize their gods with the Egyptians' raised some relevant questions for the game: Were different cultures' gods actually the same gods, or truly distinct and separate pantheons, or some combination of the two?
For the purposes of the Kynthiad, I decided early on that the Egyptian and Greek gods would be two separate pantheons. I did choose one point of overlap, inspired by the Greek story of Typhon, a terrible monster who almost overthrew the gods. One late version of this tale claimed that the animal-headed gods of the Egyptians were actually inspired by the Olympians, who had fled in fear from Typhon and disguised themselves as animals to hide in the far south. Typhon is equated with Set in this version of the story, and many English translations of Egyptian myths use both names interchangeably for Osiris's brother. For my game, I decided that Typhon and Set were indeed the same entity. Kynthia has recently learned during play that it took the combined might of both the Greek and Egyptian pantheons to stop him. This is a secret that both families of proud gods would prefer be forever forgotten--but with our heroine experiencing visions suggesting that Typhon is working free from his prison, it's one they will not be able to ignore for long.
The world of the Kynthiad is full of fictional lands drawn from Greek mythology, such as Ethiopia, Hyperborea, the Amazons, and Cimmeria. Because of their literary origins, these regions usually worship the same gods as the Greeks--or a subset of them, at least. Most seem to prefer the Olympians, but some honor Titans, Winds, or other gods instead. (Kynthia has found a second--or third?--home among the Amazons in part due to their shared reverence for Artemis.)
In other regions, such as Scythia and the Tin Isles [modern Britain and Ireland], the exact nature of the local gods is not always so clear cut. As Kynthia travels through foreign lands, I occasionally provide names and portfolios for gods worshiped in the area. I try to leave some mystery about whether those gods can be mapped to the Greek pantheon. or to any other. Very few of those gods will ever play as critical a part in the story as the Greek and Egyptian gods do, so definite answers are unnecessary for now. And for those that will, Kynthia will learn more in due time.