Bullet Bills are a bullet-like enemies in the Mario series that are shot from tall cannons called Bill Blasters. A Bullet Bill usually follows a straight direction until it hits something or flies offscreen. A stronger variant, known as the Heat-Seeking Bullet Bill, moves slower, but homes in on the player. In the original games it is completely red, but in Super Smash Flash 2 it is differentiated only by its red eyes.
In Super Smash Flash 2
Bullet Bill was originally confirmed by the DOJO!!! as an enemy in adventure mode. However, due to the newer dojos do not confirming it, its current confirmation status is unknown.