The Xaastyl are an "other standard" extra-planar entity from Rolemaster that did not physically exist as creatures in the game in the I.C.E. Age but might be relevant to The Broken Lands. They were flying octopi with 8 foot heads, beaks, and tentacles reaching 30 feet. They were known as the "Keepers of the Arcane" because long ago they traveled across all of the planes collecting knowledge, forming a vast library in tall towers containing all of the spells and magical skills in existence. They dwell in an interdimensional realm known as Phriagh. They never leave and cannot be summoned.
The curious thing about the Xaastyl is that they are almost identical to the "natural" form of Kesh'ta'kai (Fash'lo'nae), the dark god who had the greatest knowledge of magic out of anyone in the Shadow World history. The Xaastyl are part of the same category of entities that were the basis of the creatures in The Broken Lands. The premise is an interdimensional realm of vast trans-planar knowledge.
Behind the Scenes
While the Xaastyl are not apparently represented in any form in The Broken Lands, the missing text in the Iruaric glottalizations in the game forms Lovecraft's own pronunciation for Cthulhu, who was part octopus and part dragon. The missing text insinuates the phrase Luor'ka'tai, similar to Kesh'ta'kai. It might be implying his relationship to the origin of the Dark Gods with Kadaena, Orgiana, and Morgu. In this case we might assume that Kesh'ta'kai was originally a Xaastyl who ascended himself to god-like power with the methods in The Broken Lands, and that Kadaena survived by becoming Orgiana. The caveat is his bestial avatar may have been insufficiently defined in the Shadow World lore of the time to posit this relationship. It was originally described only as a hideous tentacled mass. The Lovecraft analog of the Xaastyl would be the Great Race of Yith, who had the vast library of Pnakotus, housing the Pnakotic Manuscripts. The Iruaric name for The Broken Lands is Man'ta Pn'Tairken.