Circus

Circus was a support unit that has (as of now) only appeared twice. It was specially designed to be able to fuse with Dr. Light to make a giant robot. Its only appearance was made during the Attack of X, where Dr. Light fused with Circus, but he was unable to get to X, due to the door's small size.
Dr. Light also used Circus in the storyline "All Good Things" to fight the merged form of Nate, Proto Man, and Mynd. Circus appears as a recolor of the Maverick Flame Mammoth from Mega Man X.