The Ultimate Enemy: Part 1 is the fifty-first episode of Ben 10: Ultimate Alien.
As the war between the Forever Knights and the Flame Keepers' Circle continues, several Forever Knights are attacked by a group of Esoterica, and the green weapon one of the knights was using is knocked across the ground over to Kevin. Kevin picks it up, connects his Plumber Badge to it, and uses it to continue fighting. He and Gwen are busy taking out Esoterica soldiers. Suddenly, they feel a large tremor, as Vilgax is still breaking the seal containing Diagon.
He fires at the team, however Gwen is able to shield them with a large mana field. Unfortunately, Vilgax has been able to damage the seal just enough, so that Diagon is able to produce a wave that transforms every living person on the planet into an Esoterica. Ben, Gwen, Kevin, and Sir George are not affected due to Gwen's mana field, as well as Julie, whom Ship shielded from the wave by transforming into a suit around her. Every being on Earth is now under Diagon's control.
Vilgax attacks again, with a large energy ball that breaks Gwen's mana shield. Heatblast, however, is able to use his fire to melt the rocky ground under Vilgax, and he sinks in. Vilgax is trapped; shoulder high in the rock, and Kevin tries to inform Sir George to wear his suit's helmet, as the iron in it stops Diagon from controlling his mind. George refuses, and says that Ascalon is the only protection he needs.
Heatblast tells Gwen to find a spell that can contain the Diagon, and she and Kevin go off to find one.
Heatblast then melts the rock under Vilgax, who gets trapped and cannot escape the rock. He asks his master Diagon to give him more power, so that he may free himself and break the seal. Diagon agrees and Vilgax glows blue and grows stronger as he breaks out of the rock. He attacks Heatblast and George, and Heatblast transforms into Eatle to fight him. After a long and difficult battle, Eatle is able to ram into Vilgax and send him flying. Vilgax breaks through several buildings and crashes into the top of a pyramid. While George and Eatle think that he has been defeated, Vilgax rises up and breaks the top off of the pyramid, then throws it at them. Eatle is able to cover and protect George, but the large building falls on top of them. Vilgax crosses the wreckage and approaches the seal, as he starts to destroy it.
Meanwhile, Gwen and Kevin have taken the Rust Bucket 3 back to her house in Bellwood, to retrieve a spell from one of her books with which she may be able to confine the Diagon. They are attacked by many Esoterica, and are only able to hold them off long enough to enter Gwen's house, and for Gwen to put up a large mana dome around it, to keep the Esoterica at bay and to buy themselves some time.
As Vilgax is attempting to destroy the seal, Diagon is angry at him, for the power he was given was more than enough to break the seal. Eatle and George rise from the wreckage and begin to attack Vilgax.
Gwen and Kevin are still at her house, and Gwen is disappointed to find that none of her books have any spell that could hold Diagon. The Esoterica finally break the shield, and she and Kevin are forced to flee. The Esoterica attacked them outside of her house, and Gwen and Kevin begin fighting them again (Kevin using the weapon he took, and modified during their stay at Gwen's home).
The Esoterica surround them, and Gwen tries to create a shield around them, but is mentally attacked by Diagon. She tells Kevin that her previous experience with the Lucubra's mind control has left something inside her, and Diagon is able to control her. Diagon then completely takes over her, and makes her use her powers to race towards him. Kevin gets into one of the many abandoned cars and follows her.
Eatle and George are still fighting Vilgax. Eatle mentions to Vilgax that he is not a true servant of the Diagon, and he only wants something out of it for himself. Vilgax is angered and attacks Eatle again. He successfully attacks Eatle and George, knocking them away. Ben transforms into Humungousaur and runs towards Vilgax.
Vilgax manages to knock Humungousaur away again, and he nearly falls onto Kevin, who has arrived in the car to tell them that Diagon's got Gwen.
Gwen approaches the seal, and Diagon expresses his disappointment in Vilgax's failure. He then makes Gwen transform into her Anodite form. Humungousaur approaches her, and tries to stop her, but Gwen uses her powers to knock him out, and forces him to transform back into Ben. As she begins to break the seal, Kevin runs up to her and grabs her arms, then covers her in the metal coating he was wearing, before pulling it back onto himself, with the exception of a metal cap over her head, to prevent Diagon's control. She thanks him and Kevin creates a metal cap around Ben's head too, as well as offering one to George, who refuses again for the same reason.
Gwen, George, Ben, and Kevin now corner Vilgax and demand him to tell them how to stop the Diagon from coming, and how to change everyone back from being Esoterica.
Vilgax asks his master Diagon for more power, but is met with silence. Ben remarks that he is now on his own, but a ship comes in from overhead, and Psyphon exits it. Vilgax is angry that Psyphon is late, but Psyphon claims that gathering everything Vilgax asked for took more time than expected.
Gwen, George, Ben, and Kevin approach Vilgax and Psyphon, and Ben transforms into Jury Rigg. However, a large tremor shakes the cave, and the seal glows with a bright light, as Diagon's voice booms and reveals that he has finally escaped. The seal glows brighter, then breaks apart. Both sides approach it and look into Diagon's dimension, but find nothing. They hear his booming laugh, and run out to the cave's exposed ceiling to find the giant Diagon in the sky, as he boasts that he is 'everywhere'.
- Psyphon returns.
- Ben Tennyson
- Gwen Tennyson
- Kevin Levin
- Forever Knights
- Julie Yamamoto
- Jimmy Jones (cameo)
- Mrs. Jones (cameo)
- Carol Smith (cameo)
Naming and Translations
|Hungarian||A legnagyobb ellenség, Első rész||The Greatest Enemy, Part 1|
|Portuguese (Br)||O Inimigo Supremo: 1ª Parte||The Supreme Enemy: 1st Part|
|Spanish (HA)||Enemigo Supremo: Parte 1||Supreme Enemy: Part 1|
|Spanish (Spain)||El Enemigo Absoluto: Parte 1||The Absolute Enemy: Part 1|
- The entire human population turning into Esoterica is similar to what happened in the Doctor Who episode The End of Time when all of humanity is turned into a copy of The Master.