@nightmares06 and @neonthewrite originally designed their separate species of sprites in completely different worlds, and though the differences between them are clear, the fact that they now technically live in the same Brothers Apart world means that sometimes the lines can blur.
The aeternum sprites are designed as elementals. Magic lives in their bodies and they are sustained by it as surely as we are sustained by water.
If the connection to this magic breaks, they lose all of their abilities until the connection is fixed. If the break is bad enough, the sprite in question might forever lose their ability to touch magic, and will then fade from existence. For a water sprite, the immortals of the aeternum sprites, this would be akin to being trapped in limbo for all eternity, unable to reach out past their own body.
As elementals, the aeternum sprites possess power that could crack the world. Because of this, they were given their own dimension to exist in separate from the world. Here, they are able to answer summons from the gods or humanity, but will not destroy entire countries with their ‘play.’ The air sprites especially tend to be capricious and uncaring of the lives of mortals.
Added to all this, the aeternum sprites are only female. There are no males to be found. As they arise from magic, they do not need to breed or have children. The gods have tended to these needs for them.
Earthbound sprites, the sprites that we see in the book Bowman of Wellwood, are the ones that live in peace on the planet alongside humans. They are mortal and do not directly possess magic of their own, but their creator, the Spirit of their kind, allows them to ‘borrow’ magic when in need.
For example, the sprite Rischa Songbird has a strong connection to the spirit. With this, she was able to help heal Dean Winchester when he was afflicted by the Lich’s blight. In comparison, Nixie the aeternum sprite could only heal Sam Winchester by immersing him in water and using her magic to repair the damage that had been done to his body.
Earthbound sprites, being extensions of a Spirit, are like tiny windows through which these otherworldly beings can influence the world. The Spirits can visit people in dreams, but rarely manifest in reality. The places they have touched tend to be rife with energy and are generally marked with some kind of fairy circle; the ring of trees in Wellwood is one example of this.
If someone knows how to look, they could also see the other way through these little spirit-windows. The Lich was a good example of why that’s a very Bad thing.