Bubble Lead

Bubble Lead (バブルリード Babururi-do) is Bubble Man's main weapon. It throws a heavy bubble that rolls in the floors. If used against Bubble Man in the final stages, it will recover all of Bubble Man's health. It bounces instead of rolls when used by Bubble Man.

The Doc Robot from Mega Man 3 also used this weapon along with the weapons from the other Robot Masters from Mega Man 2, but the player can't take it from Doc Robot.

Robot Masters And Bosses Weak Against Bubble Lead

 * Heat Man: Mega Man 2, Mega Man: Dr. Wily's Revenge and Mega Man 2: The Power Fighters
 * Alien: Mega Man 2

Trivia

 * There has been some debate over the weapon's real name. Some say it is Bubble Lead (pronounced led, as in a lead pencil), signifying that the bubble is made of heavy lead.  Other say it is Bubble Lead (pronounced leed, as in leading a horse to water), signifying that the bubble can lead Mega Man since it travels along in front of him, and in fact can be used to find the hidden floors in one of the Wily Levels at the end of MM2.