Hiyoko Master', known as Gachou Mecha (ガチョウメカ) in Japan, is the second boss of the 8-bit versions of Sonic the Hedgehog 2, fought at the end of Sky High Zone.
Before Sonic can fight the boss itself, he must fight two waves of Mecha Hiyokos, at which point he drops through the clouds to smash the cybernetic eggs which create them. Rolling on the clouds works well in this part of the boss fight, and do note that the eggs will still produce the Mecha Hiyokos while Sonic is attacking them.
Only when its 'nest' has been destroyed does the boss rear its chrome-plated head (on an extremely extendable neck). It proceeds to fire energy balls in Sonic's direction, which possess a limited degree of homing. Six Spin Attacks will finish it off, and if Sonic is fast enough the Hiyoko Master can be defeated without ever giving it a chance to attack.