Proto Buster

Proto Buster, known as Blues Buster in Japan, is Proto Man's arm cannon set in his left arm. It's his version of the Mega Buster. The only difference is that the Proto Buster is unable to change freely into the form of an arm like the Mega Buster can,. although in some instances, like Mega Man 7 and Mega Man: The Power Fighters, he is seen with both arms.

In Mega Man: Powered Up the Proto Buster can only shoot fully charged shots, without Proto Man having to charge up, though his mode is barely canon. In Mega Man 3 the Proto Buster shoots regular sized shots, much like Mega Man's shots. In Mega Man 7, Proto Man shoot regular shots once more. However, his charged shots are much more devastating than Mega Man's, and they took the form of a giant green blast. The Proto Buster in Mega Man: The Power Battle and Mega Man 2: The Power Fighters was brought down to normal strength shots and charge shots like the Mega Buster, and in the latter, Proto Man was able to use Proto Strike, a short ranged blast. In Mega Man & Bass, Proto Man was able to use the Big Bang Strike, which used up most of his energy. In Mega Man 9 and Mega Man 10, the buster was only able to shoot two shots on screen and it was the only one able to shoot charged shots, more similar to Mega Man's charged shots in Mega Man 4.