Code Lyoko - Season 3 - Eps 13: Final Round
After William is initiated into the group, a series of events leaves only him and Aelita to defend Lyoko's core. During William's first mission to Lyoko, Xana uses the Scyphozoa to possess him, making him the general of a massive army focused on Lyoko's core. Despite their best efforts, the group can't stop the possessed William from destroying the core, which both renders the supercomputer useless and transforms William into a darker, Xana-themed version of himself. Later, in the Hermitage, while the group broods over their predicament, Jeremie receives a coded message directly from the internet, sent by none other than Franz Hopper who somehow survived the destruction of Lyoko.
About Code Lyoko

Title: Code Lyoko
First Air Date: 2003-09-03
Last Air Date: 2007-11-10
Status: Ended
Rating: 7.463/10 (from 81 votes)
Language: FR
Seasons: 5
Total Episodes: 95
Network: France 3
Genres: Sci-Fi & Fantasy, Animation, Comedy, Action & Adventure
Production Companies: MoonScoop, Antefilms Production
Synopsis
Four children travel to the virtual world of Lyoko to battle against a sentient artificial intelligence named XANA, with a virtual human called Aelita.
Cast

Raphaëlle Lubansu
Jeremie Belpois / Odd della Robbia (voice)

Géraldine Frippiat
Yumi Ishiyama (voice)

Marie-Line Landerwijn
Ulrich Stern (voice)

Sophie Landresse
Aelita Schaeffer (voice)

Mathieu Moreau
William Dunbar (voice)

Carole Baillien
Sissi Delmas (voice)