Submarine Eggman (サブマリンエッグマン), located in Hill Top Zone, is rather simple: you just have to know what you're doing. The first thing(s) you'll notice are three islands: one on the left, one in the middle, and one on the right of the screen. In between these islands you'll find two lava pits. These lava pits are where Eggman will pop out in his heat-resistant submarine and shoot stuff at you. Simply hop on Robotnik twice when he appears, avoiding all flaming projectiles he launches at you.
If you are really risky (or if you have a shield), you can hit Robotnik eight times in the first shot; just jump on him as he comes up. Note that you will, inevitably, land on the lava and lose your rings or shield.
||Compressed art offset
||Pattern Load Cue
|Sonic the Hedgehog 2
||Hill Top Zone boss
||$8595C (Nemesis Format, 107 Blocks)