Ares

Ares is a bat that lives in the Underland. He was the once bond of Henry but later became Gregor's bond after Henry plotted a plan with the rats that Ares didn't know about. Gregor jumped into a gorge to save his friends, and Henry fell in as well, thinking Ares would save him. However, Ares saved Gregor, instead of his bond, and Henry fell to his death. Gregor bonded with Ares to save him from being executed for letting Henry die.