Lenopan

Lenopans, mostly called Sludgepuppies or Sludges, are a species of alien blob shapeshifters. Though now at peace with humanity, they have historically tried to cause trouble on Earth and had thus been in opposition with the Plumbers.

Appearance
Lenopans are capable of taking on humanoid shapes and features, such as skin and hair, or, in Lucy and Camille's case, a humanoid shape while retaining a mud-like appearance.

Female Lenopans have two mobile whiskers on their cheeks and two antennae above their much larger eyes; while males lack both. Male Lenopans usually have smaller eyes than females.

Prior to the original series
The Earth's Plumbers and the Lenopans were involved in a decades-long feud, before it was ended by the marriage of Plumber Joel Tennyson and Lenopan Camille Mann.

Ben 10
In Big Fat Alien Wedding, Joel was about to get married to his alien girlfriend, but her family objected to her marrying a human. During the rehearsal dinner, Camille's Ex-Boyfriend disrupted the reception to forestall suspicion upon the parents, but he was quickly dealt with by Ben as Diamondhead.

During the wedding, the Mann family and another Lenopan disguised as a wedding staff member interrupted it, destroying everything. Ben turned into Heatblast to face the Manns, but later in the fight, they merged into one being. The Lenopans captured and engulfed Ben, dragging him into their body. They thought they had won, but were defeated from the inside by Heatblast's heat, which dried and solidified them into a brittle mass. Joel and Camille finally got married, which put an end to the decades-long Plumber/Lenopan feud once and for all.

Ben 10: Omniverse
Roughly six years later, Lucy Mann became the first Lenopan Plumber.

Powers and Abilities
Lenopans can stretch and use their stretching to shapeshift body parts. If they stretch too far, it might result in the part falling off. They can detach their body parts, and stick them back on, reattaching them.

Lenopans can shapeshift their body parts, and sometimes themselves into other objects. Using their sludge, they can look like another shape made of purple sludge. They can also shapeshift into non-existent or imaginary species complete with unique abilities.

Lenopans are capable of regeneration.

A person can jump through Lenopans, only to be covered with slime.

Lenopan sludge is sticky, which gives them abilities like wall climbing.

Lenopans can fire their sludge as an attack.

Weaknesses
Lenopans can be harmed by water, fire, or by scattering enough of their body matter to the point where they cannot reconstitute (e.g. when Max set a Plumber gun to overload and stuck it in the body of the Bodyguard where it exploded).

Notable Lenopans

 * Camille Mann-Tennyson
 * Lucy Mann
 * Mr. Mann
 * Mrs. Mann
 * Camille's Ex-Boyfriend
 * Mann Family's Bodyguard
 * Deefus Veeblepister
 * Unknown (the Omnitrix's DNA sample of a Lenopan)

Trivia

 * According to Deefus, Sludgepuppy is an offensive racial slur, and the proper term is Lenopans, though no other known Sludgepuppy seen has had a problem with the term until Deefus made his dislike of it known in Omniverse.
 * In Big Fat Alien Wedding, Max said that the Plumbers just call them Sludgepuppies.
 * In Mud is Thicker than Water, Max referred to Lucy as a Sludgepuppy despite the fact that the Lenopans are no longer at war with the Plumbers. Lucy didn't seem to mind that he referred to her as such.