The main bosses of the Mega Man series are known as "Robot Masters". Each one has a theme, and a level to go along with that theme. For example, Gravity Man from Mega Man 3. As his name suggests, this robot is themed after the idea of controlling gravity. However, this should not be physically possible. Gravity is the result of large masses, such as planets and moons. In the game, this robot's level consists of "gravity" fields where you can fall towards the ceiling instead of the floor. If this were truly gravity, the level would not be able to "switch" gravity in specific places. Realistically, this would probably be an extremely strong magnet, but then we'd have a second Magnet Man.