Guardian

A Guardian is one of XANA's monsters. Referred to by the Princess as "a sort of digital jail adapted to the body imprisoned in it", Guardians have the ability to capture a being inside Lyoko at the time, and keep them imprisoned to prevent them from stopping XANA. XANA first used this method in Image Problem to trap Yumi and send itself to the real world in her place. Yumi was, of course, rescued. XANA used a Guardian the second time in The Girl of the Dreams to imprison Aelita, making Jeremie think that Taelia was Aelita materialized, but, once again, Team Lyoko stopped XANA's plot. The final time XANA used a Guardian was in Ghost Channel, when he created a simulation of Boulogne-Billiancourt to trap Yumi, Odd, and Ulrich. That Guardian was destroyed by Aelita. Guardians have not appeared since Season 1, probably due to the fact XANA realized their weakness and inconsistency with reality.

Guardians are nearly invincible. They, as seen in Ghost Channel, can be destroyed by Aelita's Creativity, but cannot be destroyed by the Lyoko Warrior's weapons, as they have no Eye of XANA. A much less painstaking process is to bring a clone of the prisoner in front of the Guardian, and then the Guardian, confused, will eject the prisoner out and explode in a brilliant orange flash.