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 off-screen. A stronger variant, known as a Bull's-Eye Bill or a 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 only differentiated by its eyes.
In Super Smash Flash 2
Bullet Bills were originally confirmed by the DOJO!!! as an enemy in Adventure mode's Hard and Insane difficulties. However, due to the newer dojos do not confirming it, its current confirmation status is unknown.
A Bull's-Eye Bullet Bill.
Heat-Seeking Bullet Bill in the Insane mode with an Angry Sun, a pair of Koopa Troopas and a Goomba.