Super Boy 3
|Super Boy 3
This game has unused graphics.
It's also the first installment in which the titular hero actually gets to rescue someone.
Starting at 0xD740 in the ROM is graphical data for Morton Koopa and Ludwig von Koopa, based on their sprites from Super Mario Bros. 3. It's likely that they are scrapped bosses, given that their sprites are directly after the Sledge Bro's.
The Super Boy series
|Super Boy I • Super Boy 3
|Sega Master System
|Super Boy I • Super Boy 3 • Super Boy 4