From Introduction:
This writhing mass of violent tentacles was summoned to the material plane by Narriot Zorbal, after consulting arcane oracles for a way to harass the Crystal King. Now, Zorbal keeps it in a pit inside his tower, waiting for the right moment to unleash it.
What Zorbal does not realize is that the Mass of Limbs is not unique, but part of a whole race of similar monstrosities, reproducing asexually via parasitism in various other dimensions. Their choice of hosts is almost nonsensical, for their criteria rest on occult principles unknown to the material world and unsensed by mortal humans. They breed inside of such varied creatures as dead gods, a magical fungus found in the cellars of a now-obsolete style of wizards’ tower, the minds of heretical priests exiled to the moons of Neptune, Plutonian ghostrock, and even certain inorganic crystals.
Zorbal obtained this particular specimen from powdered fungus that he scraped off the walls of a rival wizard's dungeon. He was not imprisoned long, for his servants quickly raised the ransom demanded. Once freed, Zorbal worked quickly to achieve his vengeance, but was thwarted. The rival wizard was murdered in his sleep by forces unknown — though a strange mass of tentacles was seen by local villagers leaving that area around the same time. After being tipped off by the oracles, Zorbal experimented with the now-powdered fungus, which had Masses of Limbs gestating inside it, and was much luckier than his deceased rival. He did not fall prey to the Mass of Limbs he hatched, but instead became its master!