Mega Man 10

How does Wily afford all these castles, anyway?

Unused Sprites
The game contains leftovers from Mega Man 9, such as the stage select mugshots and images from some scenes.

The Bunby Catcher enemy from Mega Man 9. Interestingly, two frames were added, it has the same purple color of Treble, and the sprites are located near a set of Treble's sprites, so it's possible this was intended to take Bass out of pits like the Treble Rescue and Beat Call, the new sprites being for when it was close to releasing Bass.