I made the above contraction for Sean following the plans found on Made by Joel. You drop a marble in a hole in the top of the cereal box and it slides down three ramps that were made from the cut off side of the box. The marbles collect on the bottom and won’t fall out if you leave a little ledge on the bottom of the box. It took me 15 minutes yet he was enjoying it for much longer. The only change I made was not building something to tilt the box back. Instead, I just taped the ramps tilted at an angle and it works fine.