In this video, he attempts to repeat Derek Muller's (from Veritasium) experiments where he drops a stretched slinky. Of course I have previously looked at this awesome video—here is my analysis of the slinky drop (along with a model).

Here are the key points to the dropped slinky.

When you let go of the stretched slinky, the center of mass of the system (the slinky) accelerates down just like a free-falling object.
The slinky itself has mass. This means that the top of the slinky is stretched more than the bottom. But the important point is the the slinky is stretched. The center of mass of the slinky should be closer to the bottom of the slinky right when it is released.