Complex sentence: At the ball, Prince Daniel pledges his love to Odile, thinking her to be Odette, which caused Odette to fall to the ground, the crystal having lost its power and she is mortally weakened.
Split into simpler sentences: At the ball Prince Daniel pledges his love to Odile, thinking her to be Odette. Odette falls to the ground, the crystal having lost its power and she is mortally weakened.