“Zapper” achievement is the one that a lot of people have missed, and since you can’t choose the episode in this game, you basically need to start over from the very beginning of this game if you missed this “Zapper” achievement.
Just in case if anyone would ask, there are two endings and each has an achievement. Once you have completed the game, click continue and you’ll be able to choose the ending again very quickly. And you can get all other achievements during the game play. Zapper is the only one you can miss.
[A little bit of spoiler]
During the game you will come to a basement which existed in your childhood memory
There’s a laundry room in the basement
There’s electrified water and a spooky toy monkey in the laundry room
Step into the electrified water and get yourself killed to get the “Zapper” achievement
Written by Kenny Rao