The 13th Age books hint at a really interesting potential origin for the Chuul. What if it went a little further and became a fully original 13th Age creature?
What if the chuuls, or ficers (from Artificers) are where the magic items of the Dragon Empire come from? They are nasty monsters that are birthed in the guts of Living Dungeons and seed them with potent treasures to lure food to their master until they eventually scamper free and take up residence in the wider world.
The magic items created by Ficers are actually their larva, sentient with their own personalities and goals and the ability to exert psychic pull on their owners. Like their Living Dungeon ancestors, magic items are living creatures with a bit of a lumpy, raw, biological look blended with whatever aesthetic their Dungeon has adopted--often resembling items of particularly grim and gothic mortal craft. Some ficers bear consistantly useful items, sometimes of a single kind (all swords, bracers or amulets for example) however more often a ficer will birth a variety of items--some very powerful, others cursed or spectacularly useless. Slowly they developing a sense of what adventurers want over long years of evolution and trial and error.
Another problem is that magic items grow and mature their whole lives, eventually growing into adult ficers themselves--monsters. Except for a few "duds" that remain magic items their whole lives, and despite the relationships they develop with their owners and their own best intentions, an adventurer's most beloved possessions can often slink off and become a powerful nemesis. The old personality of the weapon usually dies in the transformation, but occasionally it's psychic bond remains, but as a twisted weapon used by the new ficer to manipulate and trick its former owner. A rare few ficers reach maturity with their personalities unchanged, becoming useful allies that serve their companions as magical foundaries, or are magically charmed by spellcasters and kept in thrall to be studied or experimented on.