Goop

Goop is a Polymorph from the planet Viscosia.

Ben first transformed into Goop in the episode The Gauntlet, when battling against a Techadon robot.

Abilities
Goop is a shape-shifting, self-regenerating, almost indestructible green blob that weighs 200 pounds. Goop can wrap his slimy body around his foes and throw them around. Ben usually becomes Goop to avoid damage or needs a flexible form. Goop controls his slime with an Anti-Gravity Projector in a shape of a small UFO and if the slime and the UFO are separated at least two feet the slime will become inert until the UFO recollects it, though in recent appearances, it seems that he can move without it unless the button on it is turned off. The UFO can cause the slime to take any shape and even hover off the ground and nothing can cut through Goop and he can imprison someone inside of the slime, as seen in Good Copy, Bad Copy, Above and Beyond, and Primus. Goop is also able to fire off his slime, which gains powerful acidic properties upon impact as proven in Simple. Goop can use his acid like abilities to pick locks just like in the episode Nor Iron Bars a Cage where Ben, as Goop, helps him and Gwen get out of the jail.

Weaknesses
As potent as Goop is, it is plagued by the weakness of being limited to the UFO controlling the slime. If it is so much as separated by Goop by more than two feet, or turned off, the goo goes completely inert. The UFO must fly back within close range of the goo in order to reanimate it. It was shown in Primus that Goop's anti-gravity disk can be turned off with a push of a button, causing Goop to become inert. This was shown when Vilgax was tricked by Ben to turn into Goop to get the Omnitrix back. This weakness may or may not be in the Ultimatrix. This form is also not too popular with Kevin and Gwen, as they both think it's disgusting. This is/was not helped by the remark made by Ben in Vengeance of Vilgax: Part 2 ("It's a sewer, of course there's Goop down there.").

Ben 10: Ultimate Alien
thumb|200px|right|Goop's transformationGoop briefly appeared in the Ben 10: Ultimate Alien episode, Andreas’ Fault. Ben used him to pass through a dungeon cell. Goop then reappears in Hero Time to save Julie from Overlord.

Ben used Goop to escape his fans at the beginning of Deep. He was only able to get away with the help of Gwen and Kevin. Later when Aggregor stole the Anti-Gravity Projector that holds the water planet Pisciss together--really a piece of the Map of Infinity--Ben turned into Goop again to use his own in its place. Although Goop was atomized and spread throughout the planet's water, he was able to use this to pull the planet back together; he changed back into his human form right after returning Pisciss to stable condition. He made another brief apearance in Nor Iron Bars a Cage where once again he was only used to break out of a room.

Ben 10: Alien Force

 * The Gauntlet (first appearance)
 * Darkstar Rising
 * Good Copy, Bad Copy
 * Undercover
 * Birds of a Feather
 * Vengeance of Vilgax: Part 2
 * Fool's Gold
 * Simple
 * Vreedle, Vreedle
 * Single-Handed
 * In Charm's Way
 * Primus
 * Above and Beyond 

Ben 10: Ultimate Alien

 * Andreas’ Fault
 * Hero Time
 * Deep (2x) 
 * Nor Iron Bars a Cage

Trivia

 * Many times it seems like the Anti-Gravity Projector is the actual alien, while the goop is just an avatar.
 * He is the first alien that Vilgax ever transforms into.
 * When Vilgax transformed into Goop, despite the fact that the UFO produces Goop's speech, he could still speak when Ben turned off his artificial gravity.
 * Goop can fly as seen in The Gauntlet when the Techadon robot shoots lasers at him he flys up in a blobuolos state.
 * Dwayne McDuffie has confirmed that the natural species of Goop does not have the anti-gravity projector on their planet.
 * Dwayne McDuffie has confirmed that if Goop's projector is lost, the Ultimatrix makes a new one