Robot
Once you reach the part of the game where you are about to get to Sandy's house, there is a robot. Get close to him and do a spin attack. He will start to wobble. Get out of the way before he comes down. Once he is down, quickly go around him. There will be a target sign on it. Use a hammer or spin attack for more damage, or you can use a shooting attack from far away. If it does not hit the target, he will spin out of control.
500 coins...