S02E21 — Tip-Top Shape

During the school physicals, Xana possesses the school nurse, Yolande, and has her kidnap Aelita. The rest of the group beats her to the factory, but has no way to get Aelita from the far more powerful nurse. Having no other choice, Jeremie decides to test out an experiment which will give a person the same powers as one possessed by Xana. To do this, he has to activate a tower like Xana. Jeremie's towers turn green instead of red. Odd volunteers, and is enhanced by a ghost of Jeremie's design. This allows Odd to fight the nurse effectively while the others deactivate the tower. This fortune doesn't last, however. Xana is able to take over Jeremie's tower, reversing the effect of the ghost to drain Odd's energy. And on Lyoko, Xana makes everything invisible. Now the group has to deactivate not only the original tower, but the tower that's draining Odd's energy.