The Pokemon isn't there when I did the glitch. That Pokemon is required to me don't ask me any question about why I need the Pokemon.
Also, I didn’t mention it in the video, but I tested this glitch on a postgame save file as well. Still no Darkrai, and it matches up with what the dataminers have been saying about it’s encounter being locked behind event flags (basically needing the event for Darkrai triggered to have it show up).
you will be needing events for darkrai showing up.
Source (see the video and comment)