Bass Buster

Bass Buster (Forte Buster in Japan) is Bass' main weapon. In Mega Man 7 and the arcade games, the Bass Buster has the same capabilities as the Mega Buster. However, in Mega Man & Bass the Bass Buster lost the ability to charge its shots in favor of a drastically increased rate of fire and the ability to fire in 1 of 7 directions. The Bass Buster retained these changes in Rockman and Forte: Mirai Kara no Chousensha and in Mega Man 10 with the additional ability to disarm some of the enemy shields. 

Trivia

 * The charged Bass buster seems to resemble a skull