Shield Boomerang

The Shield Boomerang (シールドブーメラン) is a weapon in the first three games from the Mega Man Zero series that Cerveau constructed for Zero. It is an energy shield created by spinning the Z-Saber (mounted onto Zero's forearm) around. It can reflect most enemy shot attacks, however, it provides no protection from melee attacks, nor is it capable of deflecting exceptionally powerful moves (like those used by bosses). The Shield Boomerang can be charged to be thrown like a razor blade, flying in an ellipsis path (the path varying if Zero is on the ground or midair) and cutting through several enemies before returning to Zero. The Shield Boomerang can also be equipped with element chips, the charged attack gaining the same element as the chip.

In the first Mega Man Zero game, Cerveau only gives the weapon to Zero after he gets the Triple Rod and completes or fails in a mission. But obtaining the weapon is optional, it not being necessary to complete the game. In Mega Man Zero 2 and 3, Zero must talk to Cerveau and get the repaired Shield Boomerang (and a new rod) to progress the game.

Levels
The Shield Boomerang has to be leveled up in the first two games to reach its full potential. In Mega Man Zero 3, the Shield Boomerang has the same range as skill level 3.

Other media
In the Rockman Zero manga, the Shield Boomerang wasn't named or created by Cerveau. Instead, Zero activated the Z-Saber blades on both sides of the saber hilt and spun it around, making it look like a shield. He was also able to throw the saber/shield like the Shield Boomerang, and it was able to return to him.