Its a little box with a remote control.
With a button, you can inflate and deflate the 'slenderman' (a horrifying creepy dude, google it).
The idea is to place him in strategic locations, and using either human or AI control, inflate and deflate him when nobody is looking.
This will allow for
the impression that the slenderman is chasing.
For making slenderman appear in further distance, a popup cardboard may be faster. If you need even faster response, having the slenderman appears as a shadow may be cheaper, infact you can do this as a garden light!.