Tyria has one moon, considered a part of nature in general. Myths as a whole don't really seem to expand on it very much.

Trahearne in particular would offer his first memory of the moon: having been born in the Cycle of Dusk, one of his earliest memories would have been watching the sun set and the moon rise in the east. He'd also talk a bit about sylvari who awaken in the Cycle of Night (described as secretive and self-contained) and his three firstborn siblings who are night blooms. Maybe it's not about the moon specifically, but he would have first seen them under the light of the moon. like I said, scant lore come on guild wars two get your act together

There's one time of year where everyone's attention turns to the moon, though, and that's Halloween. It's around this time of year that the mad human king Thorn is allowed out of the Mists to play games and tell bad jokes. His presence seems to have a strange effect on the moon - when he's in Lion's Arch, the moon above the city transforms into a terrifying, madly grinning--oh lfmao yall seen this moon already?