Scylla

During the Golden Age, there was a story known of a highly talented mage that attempted to use the power of Arcane magic and combine it with that of the divine, testing it on animals and combining them into hybrid creatures, trying to find supposedly a secret to ascend themselves into a god. The story goes when the God of Magic Merlin learned of this, he warned the mage against continuing their experiments; when the mage did not heed the warning and continued, the Goddess of Animals Sekhmet cursed the mage. When they next tried to perform their experiment, the magic went wild and instead affected the mage and turned them into a horror that wreaked havoc in the city they were living in. The story ends with this creature being driven out of the town, where it disappears, only appearing to hunt down other creatures to undo what had happened to it.
Whether this story is true or not, what is known is that during the Dark Ages, a being that created monsters was discovered as the Fallen gods started their war efforts, creatures of hatred and twisted forms that knew not but to kill and hunt and many of these creatures were designed to hunt down magic users specifically. The only account of the being that creates these monsters comes from a survivor during the war who describes an enormous creature with the torso of a woman and a lower body made of the heads of different creatures tipping the tentacles of a cephalopod. According to the survivor, they were sent with a sizable force to end the tide of monsters bolstering the Fallen's armies, only to realize this being was not only creating them but controlling them. They faced something that commanded them with strategy and coordination, overwhelming them. As the survivor ran, he heard a single name spoken by the being, "Scylla." After this encounter, the Guardians and their forces would attempt numerous times to find and destroy this being only to have it either evade them or destroy those sent against it. Eventually, it came to be given a title, the Queen of Monstrosities.
When the Divine Barrier was erected, it is believed that the being known as Scylla was pushed off the material plane with the rest of the gods. However, many of her creations still exist to this day and still cause havoc in the world and continue to plague settlements.