SWAMPFIRE

Swampfire is plant-like alien with a flame-patterned head.  Swampfire has super strength, vast regenerative powers, the ability to control plant life through a type of gas, and the ability to shoot fire from his palms. His regenerative ability also allows him to alter his own body, such as tunneling underground in vine form or growing his feet to root himself into the ground. Swampfire is Ben's first transformation when the Omnitrix is recalibrated in "Ben 10 Returns".


JETRAY  

Jetray is a manta ray-like alien capable of flying and swimming faster than the speed of sound. He can fire neuroshock blasts from his eyes and tail, and the stingers on his head carry a powerful poison. He first appears in "Everybody Talks About the Weather" when Ben needed to chase after Alan Albright.


BIG CHILL

Big Chill is a moth-like alien whose wings and antennae can "fold" up, giving him the appearance of a phantom; his appearance is reminiscent of the cryptid known as Mothman. He can become intangible and invisible, and can breathe freezing vapor. He can also freeze the objects he passes through at his discretion. He first appears in "Kevin's Big Score" to chase down Kevin after he stole the Rustbucket.


BRAINSTORM

Brainstorm is a genius crustacean with the ability to control electrical energy and project force fields through thought.


ECHO ECHO

Echo Echo is a 4 foot tall white little 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, not unlike Ditto, but different in that the clones aren't linked in any way. By combining these two aspects, Ben can create the "Wall of Sound", wherein he and his clones can redirect projectiles back to their source by bouncing them off of strategically placed clones. He first appears in "Ben 10 Returns" when Ben fights a robotic dragon controlled by the Forever Knights.


SPIDERMONKEY

Spidermonkey is, as the name suggests, a six-limbed monkey-like alien. He has superhuman agility and, like a spider, can spin webs and stick to walls.


GOOP

Goop is a shape-shifting green blob that weighs 200 pounds.


HUMONGASAUR

Humongousaur is a humanoid dinosaur alien about a dozen feet tall. He has great strength and vast resistance to injury. Humongousaur also has the power to increase his own body size and mass, growing up to 60 feet in height. His strength increases as he grows, and his dinosaur features become more pronounced. His first appearance is in "Ben 10 Returns" when Ben fights a swarm of DNAliens


ALIEN X

Alien X is a mystery alien set to be introduced in "X Equals Ben Plus 2". He is only shown in silhouette.


CHROMASTONE

Chromastone is a living crystal, able to absorb energy and channel it into laser blasts. He is also nearly invulnerable to harm. He first appears in "All That Glitters" to stop a group of zombified schoolgirls.