Graviton

Graviton (グラビットン) is an enemy in Mega Man 5. It is a gravity-surveying mecha that hovers mid-air and periodically drops a red robot-destroying liquid. Gravitons appear in Gravity Man's stage and in the second stage of Proto Man's Castle. When the gravity changes in Gravity Man's stage and Mega Man is on the ceiling, Graviton will drop its fluid upward.

Rockman Complete Works database
Mega Man Legacy Collection translation:

A gravity-surveying mecha filled with robot-destroying liquid. Destroy it with a charge shot.

Hits Data Chart
Amount of shots/hits from Special Weapons it takes to destroy a Graviton.

Other media
Graviton had a brief appearance in the Rockman 5 manga.