Dohyo Master
From Sonic Retro
Mecha pig is the boss for Green Hills Zone. It bounces around the screen turning into a ball similar to Sonic. Also similar to Sonic is that it damages anything it touches while it's in ball form. You are able to tell that it is about to turn into ball form when it starts stomping and releasing steam from it's snout. There are three directions it can go in: down through the crater, straight across the crater and above the crater. When Mecha pig gets hit enough times it will occasionally roll twice in a row before it uncurls.