Aurora Horribilis

A ribbon of light flies just above the ground, its gleam flickering in and out of view as it emits a discordant tune.
Hidden Among Polar Lights. Though auroras horribilis can manifest anywhere on a world, they prefer to dance and sing within naturally-occurring auroras. When they notice admirers of boreal lights, they descend from the sky to share their songs. Unfortunately, they are unaware of the bewilderment their songs invoke in listeners and are subsequently surprised by hostile action toward them.
Terrible Harbinger. While an aurora’s direct effects on most creatures is cause for alarm, the aurora’s presence is typically a prelude to something worse. Auroras tend to attach themselves to the forefront of a wave of devastation wrought by unknowable beings. Given the nature of such beings, auroras can precede the beings by days or even centuries.
Lessons from the Void. Because auroras horribilis travel with ancient beings from the Void, they hear many secrets about the universe, which they incorporate into their songs.
An inability to understand the incomprehensible knowledge contained in their songs often induces madness in their listeners. This makes the auroras valuable to apocalypse cults welcoming the beings they herald, as well as to the desperate who seek to avert the coming catastrophe.