RoboCop Vs The Terminator (Game Boy) by Unexpected Development previously undiscovered cheat mode
Start a new game, hold SEL+B, press A to jump, repeat 10 times (make sure you completely landed before next jump). There is no indication, but if done right, press START to do a very high jump, hold A then press SEL to do a fast dash forward. Combine both to advance to the level. Hold B press START to complete current level up to ending. Hold B press SEL to increase current level index instantly. Use the last code on the Stage 3 (FACTORY PART 2) to get to the secret developers easter room.
Forgot to mention, hold SEL then press UP during the game to activate full invulnerability ;)