Quick Boomerang

Quick Boomerang (クイックブーメラン) is Quick Man's special weapon. It's a small boomerang-shaped cutter that can be fired rapidly and has short range. Mega Man can fire a couple of boomerangs with a small amount of energy. They are extremely useful against the first three Wily's Castle bosses. Although immune to the Quick Boomerang, Quick Man will immediately stop what he's doing and will be stunned momenitarily.

In the original Mega Man 2 game, the Quick Boomerang damaged every normal enemy in the game, including enemies that were normally supposed to be immune to all weapons such as the Big Fish in the third Wily stage. This was fixed in future remakes such as Mega Man: The Wily Wars.

Bosses Weak Against Quick Boomerang

 * Metal Man: Mega Man 2
 * Bubble Man: Mega Man: Dr. Wily's Revenge
 * Mecha Dragon: Mega Man 2 and Mega Man 2: The Power Fighters
 * Guts-Dozer: Mega Man 2
 * Buster Rod. G: Mega Man: The Wily Wars
 * Pharaoh Man: Mega Man 2: The Power Fighters

Bosses Immune To Quick Boomerang

 * Flash Man: Mega Man 2 and Mega Man: Dr. Wily's Revenge
 * Wood Man: Mega Man 2
 * Buebeam Trap: Mega Man 2
 * Wily Machine (1st Form): Mega Man 2
 * Alien: Mega Man 2
 * Iron Ball: Mega Man: The Wily Wars
 * Wily Machine: Mega Man: The Wily Wars

Other media
Mega Man uses the Quick Boomerang to escape from Dark Man's electromagnetic net in the episode The Day The Moon Fell from the Mega Man animated series. In the cartoon, its design has three boomerangs held in the firing mechanism. 

Trivia
Quick Boomerang is spelled "Quick-Boomerang" in the NES version of Mega Man 2 and Mega Man: The Wily Wars.