From Magical Oddities and Mysteries of the Occult
by the sometimes adventurer Glad of War
Section I.B: Betelgeuse
Betelgeuse aka Gassy is the collective pronoun for a sentient beetle horde whose given name is not pronounceable by the human tongue. The horde itself is mainly an (estimated) billion strong mass of beetles black in color. When destroyed, the beetles congeal into a rot scented, poisonous goo of indeterminate strength. Avoid ingestion or insertion. Because the creatures body explodes when targeted with revocation, I've theorized that the creature is magical and not purely physical in construction. Quasith is the basis of the beetles existence and once deprived they cease to be. The dead beetle goo is also resistant to alchemic reagents.
It is incredibly dangerous and motivated by an unceasing hunger. The only things known to have survived an encounter are the Vormyll fighters known as the Silver Foxes and the last two centaurs to have survived the Equinos infestation. It uses the relies on the following hunting tactics:
Overwhelming numbers of poisonous beetles
In my opinion, the greatest danger. Wounds should be treated professionally and small groups not equipped to wipe out an infestation of this size should flee on sight with the singular goal of smashing their way to the edge of its territory.
The raised dead which it controls with its beetles
It's exceptional intelligence which it uses to trap, delay, assemble its strength, and create illusions to lure in prey.
The beetles themselves are especially vulnerable to revocation. Physical attacks are also effective.
The dead raised by Gassy are can be stopped with revocation and physical attacks to incapacitate the corpse. Note that lightning is not an effective tool of destruction. Also, because corpses are merely inanimate objects, magical attacks that would normally trigger suppression if applied directly to the flesh do not trigger suppression on the dead, leaving Gassy's thralls open to a variety of attacks that morally inclined individuals would not normally use. When in Gassy's territory, dead allies should be burned or otherwise destroyed to prevent them from reviving as enemies.
It's entirely possible that the beetle horde is a proxy for a mind, heart, or other controlling agent that hasn't yet been seen and could more appropriately represent Gassy.
The following account of its history is a paraphrased autobiography attained through willing interrogation. The subject, however, was biding time for an attack on the interviewers, so take the following with a healthy dose of skepticism, although Gassy's nonchalant demeanor and overall confidence implies he had no reason to lie at the time.
Gassy comes from the Ruined Land and claims to been born sometime during or immediately after the war. It claims to have similar brethren of which it mentions a worm like creature and a mawed centipede like creature. Haaszander the Blackscale confirms encountering the latter herself once.
It has an suspiciously ill defined sense of self and self-identified as human when taking human form (pale, bald, gaunt, male), which suggests it identifies with the image and not the essence of the shape it took. It is capable of speaking the human tongue. It is also knowledgeable about subjects common to other sentient creatures like pillars and dragons, as well as more arcane topics like the Wraith related Dream World, though Gassy does not dream.
On the subject of pillars, it has been known to travel to pillars whose followers it wishes to feast on, like Equinos where it was last seen heading west. On the subject of dragons, it was quizzed on its familiarity and associations. It believes in the dragon creation myth, e.g. all living things descended from dragons. It claims the red dragon, assumedly Shul, as its dragon progenitor. It believes that its will...its hunger...is also the will of Shul. It is familiar with and respects the green dragon. It appreciates and seems dismissive of the white dragon, assumedly Mercayen, for providing it plenty of prey. It is not familiar with Vulsh.
Addendum 1
Brenthian analysis from the School of Though and expert analysis from Ruined Land survivors of authority like King Cyax have concluded that Gassy is a simulacrum of the Ruined Land rather than a magical construct actually from the area claimed. It is believed that he was created by someone intimately familiar with the magic that claimed the North after the war against the Westerners, quite possibly LeShrac himself.