Spoiler Alert begins on the last, and paradoxically easiest, level in the game, where you defeat the final boss and then rescue the princess in familiar but not quite copyright infringing fashion. At that point you play the game in reverse, going backwards through hundreds of levels that the tiny chili pepper hero has played, but you haven't. It's an odd approach to a platform game, and one that has to be played to be fully understood. In lieu of that, watch the video below.
While "playing backwards," you'll have to revive all the enemies that have been killed by "jumping" on them in reverse, replace all the coins that have been collected by running over them again, et cetera. That might seem simple, but because the game has already been played, you'll also have to avoid killing any enemies that the character didn't kill when he went through the first time, and you can't collect any coins that he didn't collect either. If you do, you create a time paradox and start the level over again. Essentially you need to jump and attack perfectly, in reverse, for each backwards-running stage.
Things start to get more complicated when you throw in various powers and weapons, which you have to "catch" as they shoot backwards out of the revived bodies of your slain enemies, and "unkill" the stage bosses that your character has already defeated. It's an interesting approach, to be sure, though I can't help but feel like the premise is a little let down by the execution: there aren't any timey-wimey powers or puzzles, just a lot of precise jumps and taps. The game still follows some basic conventions, in that it gets harder and more complicated as you go, even if you are going in the wrong direction. If that's your thing, Spoiler Alert is just one dollar in the Play Store with no in-app purchases.