Bouncing Bullet Bill
From the Super Mario Wiki
Bouncing Bullet Bills, also known as the Killer Three Bs, are a type of Bullet Bill that appear in Super Mario World 2: Yoshi's Island, its Game Boy Advance remake, Yoshi's Island: Super Mario Advance 3, and Yoshi's New Island.
In their original appearances, these yellow Bullet Bills are fired from unique swiveling yellow Bill Blasters, and have the ability to bounce off of any surface that they come in contact with. They only appear in Raphael The Raven's Castle and Fight Toadies w/ Toadies. They can be defeated with a stomp or a Yoshi Egg. They can also be eaten by Yoshi and spat back out to damage other enemies, or swallowed to produce an egg. After being spat out, they behave like a regular Bullet Bill.
In Yoshi's New Island, their color was changed from yellow to green.