According to Theo at the moment: "Create Creature: (11 Power / 8 Power): This power effects the creation of a lesser creature in the world. This includes non-sapient creatures such as dragons, elementals and other monsters that may inhabit the land. They may be assigned a Size (Small, Medium, Large or Colossal) that will dictate how common or rare they are. These are creatures that will not form cultures or cities." Sirens aren't non sapient, nor is Hum assigning them a Size that dictates how common or rare they are. It is Hum directly that decides how many Sirens to appoint. A Siren could be unappointed at will to return to being a normal dead soul. Part of a Siren's job does involve returning temporarily to collect souls, but they do not interact with the Natural World in any way. A dragon can burn and destroy cities. Sirens are basically just dead people given the job of collecting other dead people, neither of which are supposed to be able to interact with their old world. A God of Life could resurrect a Siren, and I don't really see any other way for a God to mess with one, nor do I see why a God of Life would bother to do so since Sirens are not necessarily Champions or anyone particularly important or powerful.