It has full descriptions of every mythological creatures origins and the folklore and legends surrounding them. For a GM, it was better than finding an actual gold piece. (Well, maybe not an ACTUAL gold piece …)
Monstropedia bills itself as the “ultimate online encyclopedia of monsters in myth, magick and legend” and has the goal of cataloging more than 5,000 creatures, legendary and imaginary, in its wiki-styled database.
As a resource for story-starved GMs — it’s unparalleled.