Its only use is to have an Ancient Key to be placed in its socket, making the Atrium's Nightmare Cycle be locked at the peak state. It can be removed again, unlocking the Cycle from its peak. If a fully-constructed Odd Skeleton is revived near an activated Ancient Gateway, the fight against the Ancient Fuelweaver will begin. The Ancient Fuelweaver can deactivate the Atrium's Nightmare Cycle by removing the ancient key. If the Ancient Fuelweaver is killed it will trigger an "explosion" that will activate after three minutes, it will renew the Ruins, you must then wait 20 days to fight the Ancient Fuelweaver again for the gateway to calm down.