If I had to pick yoga’s most complicated yoga asana—among the more commonly practiced poses—Parvrtta Parsvakonasana (Rotated Side-Angle Pose) would get my vote.
Parvrtta Parsvakonasana is a Warrior Pose, a twist and a balance pose. Its benefits are many. According to Yoga Journal, practicing Rotated Side-Angle Pose:
Strengthens and stretches the legs, knees, and ankles
Stretches the groins, spine, chest and lungs, and shoulders
Stimulates abdominal organs
Improves digestion and aids elimination