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Monster / Ben 10

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"You have all earned your demise at my hands!"
Eon: We're partners! I deserve to be in on every detail of your plan! Especially when it involves a bomb!
Vilgax: Not just any bomb! A Chronosapien Time-Bomb!
Eon: So you're going to wipe out this Ben 10 and his timeline? Nice.
Vilgax: On the contrary, the detonation won't even touch this timeline. It's designed to wipe out other timelines.
Eon: Which one?
Vilgax: All of them.
(Bomb is activated)
Vilgax: (laughs) Only this timeline will remain intact, while every Ben Tennyson not from this timeline will be destroyed.
Eon: But I'm an alternate Ben Tennyson not from this timeline! What..what happens to me?
Vilgax: Thank you for your help Eon. Your assistance is no longer required.
Omniverse, "And Then There Were None"

Since 2005, Ben Tennyson and his allies have been fighting off evil from Earth or space, and while some of their foes have had sympathetic qualities, these guys quite frankly do not.

All spoilers are unmarked. You Have Been Warned!

Multiple Series
  • Vilgax is a power-hungry Galactic Conqueror who seeks nothing more than the subjugation of all life, and the annihilation of all who stand against him. Vilgax has enslaved or wiped out entire worlds in his conquests; betrays and murders his own allies and minions; and repeatedly tries to get his hands on the Omnitrix despite its bond to Ben Tennyson, being willing to dismember and murder Ben even when he was a 10-year-old boy to obtain his goals. Vilgax has shredded any possible redeeming features he may have in his tormenting of Ben for years, and earns his status as the heroes' Arch-Enemy.
    • Original series: Vilgax repeatedly invades Earth and endangers entire cities to gain the Omnitrix, even turning a teenage delinquent into his mutated slave under threat of killing her if she disobeys. Having tricked Tetrax into helping Vilgax wipe out the alien's own race and threatened Ben's cousin Gwen repeatedly, Vilgax tries to saw off Ben's hand and rip the Omnitrix from him, uncaring of the danger of universal annihilation the device presents from such an act.
    • Alien Force & Ultimate Alien: Vilgax forces planets' strongest fighters to duel him under threat of annihilation so as to steal their powers and dominate their worlds. Conscripting Albedo to his side only to betray him and leave him to suffer in a mutated form, Vilgax plans to use the Omnitrix to transform any life he chooses into his monstrous slaves and lay siege to the cosmos. After his initial defeat, Vilgax becomes the herald of Diagon, hoping to use the ancient creature's powers to override the will of the universe with his own.
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    • Omniverse: Vilgax returns one final time to ally with Eon and detonate a Chronosapien Time Bomb. Betraying and murdering Eon, Vilgax reveals his intent to wipe out all timelines and universes except "No Watch" Ben's, simply so the powerless boy will be unable to prevent Vilgax from killing him and taking over the galaxy. Willing to annihilate countless alternate dimensions and trillions of lives, Vilgax reaches the height of his depravity in this final series' outing.
  • Zs'Skayr, aka Ghostfreak, was the power-hungry High-Ecto Lord of the Ectonurites, but desired domain over everything. Wanting the Omnitrix's power, Zs'Skayr had his DNA scanned, but his conscious ends up trapped in the Omnitrix. Upon escaping, he tries to possess Ben and violently abuses the Circus Freak Trio to force them to assist, before possessing Gwen and threatening to kill her. Resurrected after his death, Zs'Skayr plunges the Earth into darkness using mutagenic Corrodium radiation, which mutates everyone into nightmarish monsters. Zs'Skayr later betrays Vilgax by infecting Vilgaxia's populace, turning the people into Ectonurite slaves, and intends to spread his influence to the entire universe. Zs'Skayr makes his final return escaping Ledgerdomain, where he frees his minion Dr. Viktor by devouring the soul of King Xarion inhabiting his body, then stowing away as a sabotaged ship returns to his star system, where Zs'Skayr resurrects a Vladat called Lord Transyl, planning to use his DNA template to revive the Vladats to serve as his personal army, knowing fully well Vladats fed-on and enslaved Viktor's species.
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  • Eon is an evil alternate Ben Tennyson who traverses the space-time continuum enslaving the Bens of different timelines to become his brainwashed servants. After getting banished from the Race Against Time timeline, Eon tricks Ben-Prime and Ben 10,000 into using the Hands of Armageddon to free him. Eon erases several of Ben's aliens to dust, intending to eliminate both Bens so that he can create a new timeline where he is the sole Ben Tennyson. Trapped in the main timeline, Eon attempts to acquire Professor Paradox's Chrono Navigator so he can freely travel, luring Paradox over by performing a temporal brain swap between the 11 and 16-year-old Bens. Ignoring Paradox's warnings, Eon's rampant abuse of the Chrono Navigator ruptures the timestream, with Eon declaring that if he couldn't rule reality he would destroy it instead. Eon returns allied with Vilgax, where he recruits evil Bens from throughout the cosmos to attack the No Watch timeline and was ecstatic when he believed Vilgax would nuke said timeline. Eon also assists Maltraunt in his plan to rewrite reality, by gathering Time Beasts. Having endangered the entire cosmos multiple times for his own selfish goals, Eon earns a place as one of the most vile villains to ever appear.

Alien Force

  • "Vendetta": Ragnarok is a criminal who makes a living by using his ship to drain stars of their energy for profit, killing all life in the star system that depended upon said star. He attempted to do this to the Sun, before being stopped and imprisoned in the Null Void, allegedly killing Plumber Devin Levin. Escaping imprisonment years later, Ragnarok once again resumes his attempts to drain the Sun by finding the key to his ship, where at one point he sadistically beat Kevin to near-death in his search for the key, and upon finally acquiring the key he resumes draining the sun.

Ultimate Alien

  • Seasons 1 & 2: Aggregor is an Osmonian warlord who is wantonly murderous in his quest to achieve omnipotence. Aggregor killed aliens by absorbing their energy and matter to gain their powers. Generally this caused his victims to turn into desiccated husks, but for his plans to become powerful enough to reassemble the Map of Infinity, he turned five aliens into energy and absorbed them into himself. Aggregor killed Magister Prior Gilhil by stabbing him In the Back, killed two other Plumbers by sucking them into space, and absorbed the life and powers of a pacifistic alien just because he could. His two most vile crimes, however, were when he nearly destroyed an entire inhabited world by stealing a component from the device that kept the planet from breaking apart, and when he tried to kill and absorb a baby alien capable of Reality Warping to complete his ascension into godhood.


  • Seasons 7 & 8: Maltruant is a rogue Chronosapien bent on ruling all of time and existence. He masterminded the original Time War in his first bid for universal control, but was defeated and his body separated across time by Professor Paradox. Seeking to restart the Time War and win, Maltruant hired Dr. Psychobos to help repair himself. After Subdora and Exo-Skull complete repairing his body, Maltruant turned on Dr. Psychobos, easily defeated Ben Prime and Ben 23, and left both for dead in Mad Ben's dimension with his minions to restart the Time War. Once he travels to the time period of Ben 10,000 to steal the Anihilaarg and the Dwarf Star so he can create a more deadly weapon, Maltruant traveled back to the very beginning of the universe and sneaked aboard the Contemelia's ship, where he switched their Anihilaarg with his own in order to recreate the universe in his image.

2016 Continuity Reboot

  • Season 2's "Innervasion" arc: The High Override is a warlord and the leader of the Fulmini empire, who has harvested countless planets for their energy. He sets his sights on Earth after discovering its existence through Ben using Shock Rock, the Omnitrix's DNA sample of a Fulmini. At first, manipulating Ben as Shock Rock as a voice in his head before taking over his body during Ben's sleep, the High Override makes Ben construct a beacon to allow a portal to opened for the Fulmini to invade. When resisted by Ben and Vilgax, the High Override takes over Shock Rock's mind and forces him to attack his friends, while banishing Vilgax into the Null Void. One of the most dangerous threats in the show, the High Override set a serious tone scarcely seen from other villains.