Is a Methanosian from the planet Methanos (referring to Methane). Swampfire is a plant-like alien with a fire-patterned head. He is described as a living swamp. He has superhuman strength, vast regenerative powers, the ability to control plant life through a type of flammable gas, and the ability to shoot fire from his palms, which can also be used to launch his body for flight. The fire is created by igniting methane naturally produced within his body, which makes him stink. He can also produce seeds that quickly grow into vines that he can control. His regenerative ability allows him to alter his own body, such as tunneling underground in vine form, growing his feet to root himself into the ground, heal the limbs of others, or passing through prison bars. He appeared in pilot episode of Ben 10 Alien Force, in "Ben 10 Returns: Part 1" after the Omnitrix had reformatted.
Through the Ultimatrix, Swampfire becomes a tree-like version of himself with three blue gooey shells, containing a highly inflammable substance that Ultimate Swampfire uses to create fire bombs, nova blasts, and blue fire tornadoes. Ben used Ultimate Swampfire for the first time in Ben 10 Alien Force's series finale "The Final Battle: Part 2" to fight Vilgax, and he was the first ultimate form of the Ultimatrix by Ben.
Is a silicon-based life form known as a Sonorosian from the planet Sonorosia (the word "sonoros" in Galician it means "sound").[ He is a small white alien whose body is a living amplifier. He can scream at ultrasonic frequencies capable of overloading machinery and stopping projectiles in mid-flight. He also has the ability to duplicate himself like Ditto, but different in that the clones aren't linked in any way and can revert even if all duplicates aren't re-integrated, which splinters the original's personality. He can also use echolocation, and can channel vibrations to enhance his power. He can also transmit sound waves through speakers. The first time he appeared was "Ben 10 Returns: Part 2" to fight the Forever Knights's dragon robot.
As Ultimate Echo Echo, he a taller blue version of himself with green eyes and black lines on his body. In this state, Ultimate Echo Echo can now shoot sonic discs instead of sonic blasts and can use a stronger soundwave.
Is a Vaxasaurian ("sauria" being a clade of lizards, while "vaxa" in Icelandic means "grow"), a 12-foot-tall (3.7 m) humanoid dinosaur alien from the planet Terradino ("terra dino" means "dino land" in Italian). He has great strength and a thick layer of skin that provides vast resistance to injury. Humungousaur also has the power to increase his own body size and mass, using dimensional displacement (according to Dwayne McDuffie) growing up to sixty feet in height (making him Ben's second largest alien right after Way Big). His strength increases as he grows, and his dinosaur features become more pronounced, growing Stegosaurus-like plates on his back, a crest from his forehead, and spikes on his tail. Recently Humungousaur has proven to be durable enough to survive in space for at least a few minutes. His first appearance is in "Ben 10 Returns: Part 2" when Ben fights a swarm of DNAliens.
Through the Ultimatrix, Humongasaur becomes a larger green-skinned version of himself with gray horns on his head, arms, chest, back and he holds a mace at the end of his tail. He can convert his hands and fingers into missile-like weapons, and has the power to grow up to 120 feet tall. This form was first used by Albedo in Ben 10 Alien Force's series finale to fight Ben/Humongasaur, being the first ultimate form of the Ultimatrix. Ben first uses it in Ben 10 Ultimate Alien episode "Too Hot to Handle" to fight P'andor and his minons (Surgeon, Hammer and Buzz).
Is an Aerophibian (a play on "aero" for air and "amphibian") from the planet Aeropela.Jetray is a manta ray-like alien capable of flying and swimming as fast as XLR8, being able to reach significant fractions of light speed. As Jetray, Ben can shoot neuroshock blasts through his eyes and tail, which are strong enough to carve through stone. He can also breathe in water and the depths of space. Jetray first appears in "Everybody Talks About the Weather" when Ben needed to chase after Alan Albright. Jetray was the last alien that Ben uses in Alien Force.
Is a Necrofriggian ("necro", meaning death, and "frigid", meaning very cold) from the planet Kylmyys (the Finnish word for coldness).A moth-like alien, Big Chill's wings and antennae can fold up into a cloak of sorts, giving him the appearance of a phantom. He can become intangible, fly, has superhuman strength despite his frail appearance, and can breathe freezing vapor. He can also freeze the objects it phases through at his discretion. He can also make ice beams from his hands, and control the flow of these beams. Counter-intuitively, Big Chill is easily capable of withstanding extreme heat, at one point drinking molten metal directly from a massive smelting cauldron. Necrofriggians are also known to asexually reproduce, laying a vast number of eggs every 80 years. During its reproductive cycle, the Big Chill persona takes over Ben's body and eats metal objects, and causes him to act in a manner not unlike a pregnant female. Ben does not remember anything he does as Big Chill during the cycle. He first appears in "Kevin's Big Score" to chase down Kevin after he stole the Rustbucket.
Through the Ultimatrix, Big Chill becomes red-skinned version of himself. In this state, Ultimate Big Chill can now also create "ice flames". He was first seen in "Hit Em Where They Live", to fight Vulkanus.
Is a Crystalsapien from the planet Morotesi (which is the Turkish word for ultraviolet, his name is a pun on chromatics, the science ofcolors, and stone). Chromastone is a super dense silicon life-form able to absorb energy like a conductor and channel it into laser blasts or less-intense natural light. He can also allow it to pass harmlessly through his body via refraction, or can be blasted back at the foe. Chromastone can seemingly produce blasts without having to absorb energy, though it may be due to absorption of radiant energy like sunlight, or streetlamps or just ambient energy. Chromastone first appears in "All That Glitters" to stop the zombies. During the episode "Vengeance of Vilgax: Part 2", Chromastone was seemingly destroyed by Vilgax, but the alien's remains reformed into Diamondhead. However it would be later revealed that Chromastone was means for its genetic donor Sugilite to hide in until the time came for him to restore Petropia. Although Chromastone becomes accessible again after the events of "The Secret of Chromastone", Ben did not use him until the pilot episode of Ben 10: Ultimate Alien, called "Fame", to fight Bivalvan, being very surprised he was still in there.
Is a Cerebrocrustacean (a play on "cerebrum" and "crustacean") from the planet Encephalonus IV (a play on "encepha-", a prefix referring to the brain).Brainstorm is a genius crustacean alien with the ability to control electrical energy and project force fields around himself and others through thought, accomplished by opening the exoskeleton plates on his skull. He also has the power to levitate, and create electricity from his pincers without needing to open his skullplates as well. In this form, Ben speaks with much greater diction and with a British accent. He was first seen in "Pier Pressure", to face Ship, but Brainstorm was an accidental transformation.
Is an Arachnichimp (a play on arachnid and chimpanzee, Spidermonkey's name is also an obvious pun on spider monkey) from the planet Arahnascimmia (can also be called "Arachna", said by Simian) . As his name suggests, he is a six-limbed monkey-like alien, with four green eyes, hairy body, and a line coming out from his Omnitrix symbol to his back. He has superhuman agility and, like a spider, can spin webs that he can swing from or create spider web from his tail, and stick to walls. Spidermonkey first appears in "What Are Little Girls Made Of?" to face his grandma Verdona.
Through the Ultramatrix, Spidermonkey becomes a bulky gorilla with four spider legs sprouting from his back. In this state, Ultimate Spidermonkey is stronger and can spit webs from his mouth. He was first seen in the pilot episode of Ben 10 Ultimate Alien, to fight Bivalvan.
Is a Polymorph (a word meaning "many shapes") from the planet Viscosia (a play on "viscosity").He is a shape-shifting, self-regenerating green blob that weighs 200 pounds. Goop controls his slime through an artificial gravity generator, like a small UFO that has a button on it that turns him off. The gravity generator allows the slime to take any shape and levitate. However, if the ship and the slime are separated by even a short distance, the slime will become inert until the ship recollects it, as shown in the episode "Primus" when Ben gave Vilgax the Omnitrix and turned him into Goop except Ben turned off the gravity mode on the gravity generator.
Goop's slime can be made acidic, and the ship's edges have been shown to be sharp enough to cut through material such as Swampfire's body. Goop first appears in "The Gauntlet" when Ben battles a Techadon.
Is a Celestialsapien ("celestial" referring to a supernatural being and "sapien" meaning "wise" in Latin) from the planet Zvezda (meaning "star" in the Bulgarian language, Russian language, Serbian language and the Slovenian language, or "knowledge" from veda in Sanskrit). As its name implies, Alien X is the tenth alien that Ben becomes. Alien X is capable ofwarping reality at a whim. He has a black body covered with tiny white stars, black feet, green eyes, and three horns protruding from his head. Alien X possesses three distinct personalities:
Serena- The voice of love and compassion.
Bellicus- The voice of rage and aggression.
Ben Tennyson- The voice of reason.
All three speak in unison when Alien X speaks. For Alien X to perform any action, including but not limited to simple movement and transforming back into Ben, two thirds of Alien X's personalities must agree to do so. As both Serena and Bellicus have been arguing for an eternity, and before Ben had no tiebreaker, getting them to focus on any present task is difficult at best, leaving the body of Alien X frozen in place while Ben attempts to convince them to act.
Is a Biosovortian. He has the power to create magnetic fields, enabling him to repel, attract, and control metallic objects. In the episode "Busy Box," it is also shown that he can emit magnetic pulses. Dwayne McDuffie also says he has super strength which is yet to be demonstrated. Lodestar is introduced in the third season episode "Simple", though his hologram is seen at the end of "War of the Worlds" when the Omnitrix resets itself. Lodestar has black skin with yellow stripes, large, spiked shoulders, and pincers for hands. His head, which pivots on magnetic fields, seems to be made of large, bent rectangles of metal, with green eyes. His head levitates between his shoulders, which is held in place magnetically.
His name is a play on lodestone, a magnetic iron ore.
Is a miniature carbon-silicon-based life form, introduced in the film Ben 10: Alien Swarm. He is a Nanomechian from the hive planets. He can fly and shoot energy bolts. He can also alter the size of his body to adapt to any situation. Being a part of the chips' hive mind however renders him vulnerable to the Queen's link to the other chips, though unlike the drones he retains his individuality. It's worth noting he is drastically different than the source alien, which are insect-like while Nanomech takes on a humanoid shape.
He appears for the first time in the cartoon series in the Ben 10: Ultimate Alien episode, "Video Games", with his appearance and voice changed. Ben transforms into him so that he could be in a supposed video game he was going to be in. Later in the episode, he was used to tear apart the insides of Will Harangue's robot.
Is an Appoplexian (a play on "apoplexy", a part of the brain that deals with anger) from the planet Appoplexia. His appearance looks like a large, musclebound, humanoid tiger with no tail. Apparently, Rath's species suffer from heightened aggression and decreased intelligence, having a need to fight anything that breathes, making Rath just as likely to attack or provoke his friends as well as his foes and as a result alters Ben's personality the most among his aliens. Rath always refers to someone by using both their first and last names regardless of the situation and his mannerisms and speech are reminiscent of a professional wrestler. Rath has a tendency to say "Let me tell you something!" followed by the full name of whoever he's talking to.
However, Rath is more than able to back up his threats and is one of Ben's most powerful aliens, as his species is gifted with enough physical strength to easily lift objects far larger than him and pummeling most of Ben's enemies with ease. In addition, Rath has a retractable claw on his wrist that can generate shockwaves when driven into objects and Rath is also durable enough to survive for short periods in space and take a powerful laser cannon blast at point blank range without even flinching or reacting. His claws are sharp enough to cut a huge rock into two with ease.
He was first introduced in "The Con of Rath" (a play on "Wrath of Khan") when the Tiffin of Luoda sets off a circuit in the Omnitrix.