9. Resetting The Computer... Literally - X-Men
X-Men is regarded as one of the toughest Mega Drive games due to its unfairly placed platforms and relentless enemies. Even if you memorised every jump and could counter every villain's attack, gamers tended to get stuck on the penultimate level, Mojo's Crunch.
After you destroy the screen at the end of the area, you'll be instructed to "Reset the computer now!" to face Mojo. After exploring the area, you'll be mystified to learn that there are no switches or levers to restart the machine. Players scoured for hours, seeking a reset switch, not acknowledging there was one in front of them the entire time.
When the screen tells you to "reset the computer", it means you need to press the reset button on your Mega Drive! If this puzzle was in the first or second stage, the player might consider resetting their console. But since Mojo's Crunch is the second-last level, nobody wanted to risk losing all their progress up until that point.
You have to commend the developers for concocting such a clever brainteaser but it's baffling that they thought players would figure it out without help.