Code Lyoko - Season 3 Episode 13
Final Round

After William is initiated into the group, a series of events leaves only him and Aelita to defend Lyokos core. During Williams first mission to Lyoko, Xana uses the Scyphozoa to possess him, making him the general of a massive army focused on Lyokos core. Despite their best efforts, the group cant 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.