Practicing straddle L to endo presses on beam is a good drill to develop balance, body control and strength. One of the gymnast's goals must be to show a good straddle L, and also move in and out of that position with as much compression as possible.
The inside endo starts with the gymnast beginning to pike as the body is already bailing over, and keeping the shoulder angle as open as possible while the pike compression increases. Aiming to get the feet between the arms and the rail cleared before the hips, the center of mass moves down lower than a horizontal line with the bar.
The gymnast demonstrating this combination bails over with a little arch to begin the inside endo, but then shows a good compression, and on the swing up and comes out of the skill with the correct hip roll-out action. On the pirouette to mixed grip he again has a slight arch that could be refined to a straighter position and keeps his head slightly out to maintain visual contact with the rail during his pirouette which helps him to regrasp the bar more consistently.
In general, one of the most common learning mistakes of either straddle or inside endo to full pirouette is to swing down crooked after the pirouette. The reason for this mistake is an excess of support transfer to the post arm. The gymnasts shift their weight like they were going to perform the regular front pirouette that they have learned before, and that really requires a support transfer beyond the vertical of the post arm to finish square in a different bar position.
As mentioned before for the endo to mixed grip full pirouette combination, some of the gymnasts' main goals are to clear the rail, to flow from the endo to the pirouette without a large pause, and to swing down square. Notice how the gymnast keeps his eyes on the bar during the full pirouette.
Begining with an undergrip during the front part of the swing the gymnast brings the legs to a deep pancake in which the body passes through the bottom and is kept during the swing up while the athlete initiates a strong straight arms pull to support. The support ends with a wrist shift while the legs move out of the pancake compression.