Mechanical Enhancement.

Unlike her standard servants, the Queen Below needed to use more extreme means to elevate the geargnaw to the level necessary to serve her. Thus, she used her vile magic to warp the powers of Mechanus and pull them into the Fey. As these gears and gizmos felt the power of chaos for the first time, she implanted them into the greatest beaver in her domain and spawned the Architect. He surged with a newfound genius intellect and got to work. His first task? Grow his labor force. His second task? Build a grand palace for her majesty. Now, the Queen Below uses the Architect and his geargnaw workforce to work on the most important constructions in her realm.

Gearcanthropy.

This is the methodology by which an ordinary creature, often an unintelligent beast, becomes infected with microscopic mechanical components that potentially increase both its intellectual and physical capacities. While the name is reminiscent of lycanthropy, this is far from a curse or a disease. Instead, gearcanthropy is a corruption of the Order of Mechanus, a perversion used in the service of the Queen Below. Gearcanthropy turns infected creatures into half-mechanical beings; in the case of the geargnaw, it elevated their intelligence from that of mere beasts into true and intelligent denizens of the feywild while improving upon their natural architectural skills.