The Bloodworm Comet is a heavenly body that is often considered an ill omen because it appears shortly before disastrous events such as war.
The Bloodworm heralded the arrival of Lyras in 393 AV. Moon Mages received recurring visions of its appearance in the constellation of the Mongoose and its relationship to ongoing events. The Mongoose, being a Spring constellation, was out of season at the time, though visible to Celestians through a cantrip.
The Mongoose, symbol of Rutilor, defender of the Gods, is a cluster of twelve stars perched near The Cobra whose outline gives the appearance of a small mongoose with beady red eyes. A thirteenth bright, crimson star can be seen in the center of those stars, though it isn't taught as part of the constellation.
Unfortunately, you know that the anomalous object is not a star. The Bloodworm Comet, a powerful portent of chaos and upheaval, has returned to Rutilor's sign. The prophetic meaning of the constellation has taken on an uneasy quality, like the rumbling of a deep drum.
From The Study of Omens and Celestial Portents by Pentaith Illistim
And finally, one of the greatest, and most frightening, omens. The Bloodworm Comet. The Comet is seen against the constellation of the Mongoose, emblem of Rutilor. I was first alerted to this phenomenon by another astronomer, Penelope, who had been studying Bloodworm for centuries. She was an old woman, who remembered well the days of the great Empire of the Seven Pointed Star.
Penelope truly was one of the finest scholars our Guild has ever known. She taught Amiss DeRhi, famous as a seer and magician, and Taramaine Ennis-Braun, the Guildmaster Prime (or Grandmaster, as some prefer to call the position) of the Moon Mage Guild. Her loss still is still a grave wound to us all. I have since kept a close watch on the comet since Penelope's death, continuing the magnificent research that she began.
The Bloodworm is an ancient omen. What it foretells is a frightening thing. When the Bloodworm appears, the power and existence of the gods themselves will be challenged. This is why it appears in the constellation of the Mongoose, as Rutilor is the defender of the gods. Penelope said she had never discerned if the Bloodworm came about as a result of this "challenge", or if the comet somehow caused it.
The last appearance of the Bloodworm was during the time of the Empire of the Seven Pointed Star. The Emperor then was a man by the name of Chezarek. Imperial rule was not enough for this ambitious man, as he knew that in seven years he would be forced off his throne, his power lost. So Emperor Chezarek made a pact with a demonic force. He would release the force, in exchange for great power. However, once free, the demon killed Chezarek, and very nearly destroyed the Empire. The Bloodworm Comet watched it all from its throne in the heavens. As of the time of my writings, we still do not know for what reason the Bloodworm is currently here, but we do know the comet will not go until its purpose is fulfilled.