Spore: Flying Polyp

From the works of H.P. Lovecraft:

The race of flying polyps descended from space to the surface of prehistoric Earth, where they preyed with impunity on all life and dwelt in windowless cities of basalt. Later, they were warred upon by the Great Race of Yith and forced into underground caverns.

Their forms phase in and out of invisibility, but their location is always given away by the whistling sounds they make. They can generate winds strong enough to kill, and move by flying or walking on five-toed stalk-like limbs extruded from their bodies.