Labyrinth Zone boss (8-bit)
From Sonic Retro
Sonic begins underwater in this level, however he has an unlimited supply of air. When you reach Dr. Robotnik, you will notice two banks on either side of the screen. there are three spaces in which Robotnik can emerge: one on the bottom, and two on the top at left and right sides of the screen. Robotnik appears from one of the gaps. Jump on or under his pod to deal damage, but watch out! If Robotnik emerges from the bottom space, he will shoot energy balls at you. But if he appears from either of the top spaces, he will send a vaguely-homing torpedo towards Sonic. These attacks are easily dodged, though good timing is necessary due to reduced mobility underwater. After 8 hits, his craft explodes.