Goop

Goop is a Polymorph alien from the planet Viscosia.Ben first transformed into Goop in the episode The Gauntlet, when battling against a Tecadon 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 a short distance the slime will become inert until the UFO recollects it(sort of like Lodestar's head, sort of). 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.

Ultimate Alien
Goop appeared in the Ben 10:Ultimate Alien intro so he will probably appear in a future episode.

Alien Force:
The Gauntlet (First appearance)

Darkstar Rising

Good Copy, Bad Copy (used by Albedo and Ben)

Undercover

Birds of a Feather

Vengeance of Vilgax: Part 2 (Escaped)

Fool's Gold

Simple

Vreedle, Vreedle

Single-Handed

In Charm's Way

Primus (Used by Vilgax)

Above and Beyond (Last appearance in Alien Force)

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 there's goop down here.")thumb|300px|right

Translations

 * Italian: Mutante / Mutant
 * Brazilian : Gosma / Goo