A Bill Blaster is an object that shoots Bullet Bills in many games in the Mario and Yoshi series. They look like a two-sided gun, planted in the ground. They can shoot left or right; it depends where the Yoshi is standing.
In Super Mario World 2: Yoshi's Island, Bill Blasters are green. When ready to shoot a Bullet Bill, the Bill Blaster would expand in volume and then would return to normal after shooting the Bullet Bill. They can be destroyed with a Special Blue Watermelon or a Yoshi Egg.