Mephistopheles ordered Callisto to kill Julius Caesar and make Xena follow the path of peace that Gabrielle was following at the time, in order to have a chance of resurrection. She failed and inadvertently caused their deaths, which led to Mephistopheles turning her into an Archdemon (as either a promotion or punishment, depending on perspective). Mephistopheles remained silent during Callisto's subsequent redemption and a demonic Xena's failed invasion of Heaven – it is not clear to what, if any extent, these events fitted into his plans.
Some time during Xena and Gabrielle's 25-year sleep, Mephistopheles opened a portal to Hell in Cyrene's tavern, releasing the minions of Hell onto the village. The townspeople believed Cyrene to be mad, when they became convinced that the spirits came from her. They burnt her at the stake as a witch, in a false belief that it would rid Amphipolis of the spirits - but it didn't.
When Xena, Gabrielle and Eve returned to Amphipolis after the 25-year sleep, they discovered Cyrene's tavern to be filled with evil spirits. Upon finding her mother's charred remains, she vowed to return Amphipolis to it's normal state and avenge her death. Mephistopheles could not be beaten in Hell or the Spiritual Realm and so he had to be bought to the surface world. He requested a mere droplet of the Messenger of Eli, Eve. She was more the willing to spill blood to allow Xena to defeat and end his reign of terror. Once on the surface, Mephistopheles and Xena fight. He tells her that if she were to kill him, then she will take his place as the rightful ruler of Hell - a fate she was willing to take. She impales him with her sword and begins to fall victim to the grasp of the prophecy.
In order to avoid her inevitable fate, Xena hatched a plan to force someone else to take her place - namely an Archangel, Lucifer. She forced him to cave into the Seven Deadly Sins, which made him transform into a hideous beast and become the new King of Hell.
Being the king / ruler of hell, Mephistopheles was very powerful like the earthy gods or as powerful as Zeus himself, so the Powers and Abilities of the mephistopheles are similar to the powers of Hades, such as necromancy, demon control and manipulate souls. Apparently Hades and Mephistopheles, know the existence each one.
- During the final season of Xena: Warrior Princess, Mephistopheles replaced Poseidon in the opening credits when the narrator mentions "ancient gods".
- Although Xena, Gabrielle and Eve immediately know who Mephistopheles is upon hearing his name, he has never been mentioned before. This is especially odd considering that they didn't even know Heaven and Hell existed until they actually wound up there.
- Mephistopheles is the name given to the devil in the Faust legends. The origin of the name is unknown, but seems to derive either from an Ancient Greek phrase meaning "not a lover of light," (me-, a negation; phos, "light"; and philis, "loving") or from the Hebrew words mephitz ("destroyer") and tophel ("liar").
- The antagonist of "Be Deviled", who took the form of Serena and asked to be referred to as "Sin", may have been Mephistopheles in disguise.