Biting Bullet Bill
From the Super Mario Wiki
Biting Bullet Bills are unused enemies in the game Super Mario World 2: Yoshi's Island. They still make a later appearance in the level Endless World of Yoshis of the Game Boy Advance port, Yoshi's Island: Super Mario Advance 3 where they are a sub-species of Bullet Bills that only appear in one level. They are dark red (their Bill Blasters are also this color). These Bullet Bills, as their name suggests, attack by biting. A bit like Missile Bills, they chase after Yoshi. If it hangs around for too long, it will disappear. Biting Bullet Bills can be defeated by simply swallowing them or jumping on them. When Yoshi spits this enemy back out, it looks like a regular Bullet Bill, but it flies downwards.