Back layout 2.5
Until 2017, the back 2.5 was really the only viable dismount for twisty gymnasts uncomfortable with doing a double salto off the end of the beam. At D, you could get away with it.
Now, many many of the gymnasts who used to perform a 2.5 have decided to step back down to the 2/1 because they’re no longer punished for doing a C element. As a result, the 2.5 has dwindled in its popularity, also illuminating that it’s really quite difficult to do this dismount cleanly and under control and rarely worth it for just a D. Sticking a 2/1 is going to end up garnering a higher final score for nearly every gymnast.