Goop

Goop is a Polymorph alien from the planet Viscosia.

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

Abilities
He 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. Goop's voice comes from his UFO. 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 when he just transforms and says the first two letters and hits the ground.

Weaknesses
As potent as Goop is, it is plagued by the weakness of being limited to the very vicinity of the UFO controlling the slime. If it is so much as separated by Goop by more than two feet, 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's body 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 Ultrimatrix. 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 goop's down here.")

Ultimate Alien
Goop briefly appeared in the Ben 10: Ultimate Alien episode, Andreas’ Fault. Ben used him to pass through a dungeon cell. Goop then reappers in Hero Time to save Julie from Overlord

Alien Force

 * The Gauntlet 
 * 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 

Ultimate Alien

 * Andreas’ Fault
 * Hero Time

Translations

 * Brazilian: Gosma / Goo
 * Bulgarian: Слууус / Goo
 * Italian: Mutante / Mutant
 * Norwegian: Guff
 * Polish: Plazma / Plasma