Cave Wisp

Cave ghosts are default-incorporeal creatures that look like lampreys with wings, but with far more and far stronger teeth. These cave ghosts flourish the deeper they are underground- they are faster, eat more, reproduce faster, and live longer the further they are below sea level. They eat minerals, typically manifesting physically and latching onto rock to slowly grind away that precious stone. In order to manifest physically, they need a space large enough for them, like a crevice, gap, or other open space. They do not need oxygen or air, only mineral. They can enter into a hibernating stage as larvae, where they do not require food but have basically no action or agency- just floating in a direction until they die or hit a space they can begin feeding in. They can last 10 years in this phase before being sucked into the Dream Plane, where they can take the form of any kind of fish (but with wings) in a blissful fish-LARPing eternal existence in between dreams.
In order to find a mate when everyone is invisible and in rock, cave ghosts can release a low, barely audible Deep Song that emanates through miles of stone while they eat. As for defense, cave ghosts are not aggressive but can turn incorporeal and fly away, which is better.
I distribute cave ghosts evenly across the East main continent and in a big cluster under the central mountains in the West