Hookbill the Koopa.

Hookbill the Koopa is a Koopa Troopa, and a boss in World 4 of Super Mario World 2: Yoshi's Island. To beat Hookbill you must hit him on the head with eggs, thus making him tip over. Now ground pound his belly. Do this 3 times to defeat him. He also appears in Tetris Attack as Yoshi is entering Bowser's castle.