The fifth floor's Phase One enemy, gnomes holding the Air castle high against the dome that the crawlers must storm to descend.
The Dirigible Gnomes are named in the floor's opening banner as "Phase One of Four: The Gnomes," and hold the Air Quadrant castle — a tiny speck brushing the Necropolis of Anser's dome ceiling, unreachable without flight. They are one corner of the three-way standoff with the Dromedarians and Bactrians, and taking their high castle is the party's central Air-Quadrant problem, since the family cannot fly and must devise a balloon, airplane, or way to bring the castle down.
Not yet seen up close; airborne gnomes associated with dirigibles, holding a castle high in the dome.
The Air Quadrant's castle-holders and the floor's declared Phase One antagonists.
Also appears in books you've already read — spoiler-safe to their endings: