Sonic the Hedgehog 1 (REV00) Japanese Mega Drive - secret code
What's going on: these manipulations unlock the secret screen, which makes no differencce to the game though. According to legends, the actual game developers made this secret screen with their names with a special code needed to show.
Sonic the Hedgehog revision 00 only (01 wouldn't work);
Japanese NTSC Sega Mega Drive model only;
on the title screen press C, C, C, C, C, C, C, Up, Down, Left, Right. You will hear the ring sound if it's worked;
wait until the SEGA intro appears;
on SEGA screen press and hold Down, A, B, C until the secret screen appears.
You can force the SEGA screen by holding this combination during the end of the demonstration.
If done right the secret credits screen will appear, after which the "press start button" line would become visible.
P.S. REV00 draws the TM sign on Japanese and USA/EU consoles. REV01 has no TM sign on Japanese console — it's only presented on USA/EU. So you might know whether you have the right version of the game.
Video made by Valet2.