YouTube has amended its policies in regard to content that depicts dangerous challenges and pranks. Videos that encourage or show activities that could lead to physical harm, make people think they are in danger, or show pranks that could be upsetting to children, have all been banned. The recent popularity of the so-called "Bird Box Challenge" is believed to have been a contributing factor to the updated policy.
https://www.notebookcheck.net/Dangerous-challenges-and-pranks-join-porn-and-hate-speech-on-YouTube-s-banned-list.395016.0.html