Hello, I made a video for all the achievements. I speak German but you don't need to hear my voice to follow the video. You can mute me or just activate the translator.
1. Talk to the ghost boy next to the slide 01:01
2. You have to put the ball in his basket in the school yard 02:21
3. Go to the door that opened, climb the ladder and interact with the knife to your right 02:35
4. leave the room (you will see a orange ghost) to get your achievement. 02:52