You probably already know the value of hip thrust variations, but here's how to put them together into a logical progression.
Note that in the video, a small dumbbell is placed on the side of the non-weight bearing leg – the elevated leg – for the one-leg hip thrust. If you're using a light dumbbell, 15 pounds or less, you can place it on either side. However, if you're using a bigger dumbbell, 20 pounds or more, it's best to place the dumbbell on the weight-bearing side.
Matt Phelps is hugely pissed about the term "failure" and what it really means. He thinks exercise physiologists have one idea while the guys in the trenches, i.e., the guys in the gym, have a different, more realistic idea.