The Reverse salamander is a great way to improve muscle function of the core in a rotational manner.
As shown here when I drop my hips to the left; my torso is in left rotation in relationship to my lower extremity. To get my hips back up to my starting position, I must use my trunk right rotators which includes primarily the right internal Oblique, left External oblique, and left Multifidus. This exercise will work on the anterior, posterior, lateral, and spiral movement slings.
I initially show this exercise demonstrated with support of the foot. This is a regressed version of the exercise and will decrease the demand placed on the core.
I progress this exercise by elevating my entire leg to allow myself to ONLY make contact to the floor with my hips. (This is harder than it looks!)
This requires adequate mobility in the transverse plane; if mobility/tightness is limiting you form lowering your leg all the way down, just work within your given range of motion.
NOTE: Try this exercise! It is more difficult than it looks! Make sure to do this exercise slow and controlled.