Boomerang Cutter

Boomerang Cutter (ブーメランカッター) is the weapon that X obtains from Boomer Kuwanger in Mega Man X. It fires horn-like boomerangs that fly in a short arc before returning to X (the arc is upward if X is standing and downward if he is in the air). X recovers any weapon energy used from cutters that return without being destroyed. The cutters can be used to grab far away items and will sometimes return weapon and life energy from defeated enemies. When fully charged, four larger boomerangs spiral outward diagonally from X's position. This weapon is Sting Chameleon's and D-Rex's weakness. 

Trivia
Strange, because this is the same weapon was also used by Cancer Bubble, in Star Force Series.
 * If used against Flame Mammoth, the Boomerang Cutter will cut off the Maverick's trunk, disabling his Fire Wave. Similarly, if used against Launch Octopus, the cutter will slice his tentacles, disabling some of his missiles.