Mawaru C

Mawaru C is an enemy from Mega Man 11. It's a rotund greenish robot that rolls around inside a wheel-shaped vehicle that has one small opening. The outside of Mawaru C's vehicle is completely indestructible, so the only way to destroy one is to aim for the opening, which can be made easier by using the Speed Gear so you have a larger window of opportunity to shoot at the opening.

Gallery Description
A roller robot designed to flatten uneven ground. Its tough shell lets it ram into walls all day without suffering damage, but sometimes it loses control and plummets into pits.

Location: Block Man's Stage (And Others)