You know the ones, such as those back in the 16-bit era and especially the 8-bit era. There you are, possibly with a friend, and you two are about to finish off the final boss. You land the killing hit, you get to see the ending, and then you find out it is just a "bad ending," or a "false ending," and that you have to play through the quest AGAIN to get the good, true ending of the game. No, this isn't an extra quest like in Mario 1 or Zelda 1, this is a REQUIREMENT if you want to see the true conclusion to the game. And usually you don't even get to save nor get a password to continue with, no, you have to play through both times without being able to suspend your play-through meaning no switching off the power. And if the developers wanted to make it extra arduous, they also tossed in a requirement to complete some crazy extra task along the way to make it happen, or you would have to start over yet again. (Yeah, I'm referring to Bubble Bobble here.)
Let's call out some names here. Which games have this hidden trickery within them?