Bubble Lead

Bubble Lead (バブルリード) 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. It's Heat Man's weakness, but Heat Man is immune to the Bubble Lead when he's fully ignited or when doing his fire chrage attack.

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
 * Buster Rod. G: Mega Man: The Wily Wars
 * Fire Snakey: Mega Man: The Wily Wars

Robot Masters And Bosses Immune To Bubble Lead

 * Air Man: Mega Man 2
 * Buebeam Trap: Mega Man 2
 * Mecha Dragon: Mega Man 2
 * Metal Man: Mega Man 2
 * Quick Man: Mega Man 2 and Mega Man: Dr. Wily's Revenge
 * Wood Man: Mega Man 2
 * Enker: Mega Man: Dr. Wily's Revenge
 * Wily Machine: Mega Man 2 and Mega Man: Dr. Wily's Revenge
 * Buster Rod. G (2nd Encounter): Mega Man: The Wily Wars
 * Hyper Storm. H: Mega Man: The Wily Wars
 * Wily Machine 1 and 2: Mega Man: The Wily Wars

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. Others 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. The Japanese name of the weapon is pronounced in this latter way.