Bivalvan

Bivalvan (a play on bivalve, a term for clams and oysters) is a member of the Orishan species from a unknown planet in the Andromeda Galaxy. His DNA has provided Ben the form of Water Hazard.

History
He was first seen in the Ben 10: Ultimate Alien premiere, Fame. Every night he would rise out of the ocean and raid NASA, stealing equipment from their secret rocket project. Ben, Gwen, and Kevin attempted to stop his latest raid, but Ben's Ultimatrix detected that his DNA was uncatalogued in Primus' Codon Stream and went into sample mode (Bivalvan then complimented "What did you do?!"), Kevin and Gwen fought him and were beaten. He was working on the damaged escape pod underwater because he wanted to go home.

Ben attempted to fight him without the Ultimatrix, but it didn't work well. Finally, the Ultimatrix finished obtaining a sample of his DNA and allowed Ben to transform into Chromastone, who unfortunately, was defeated just as quickly. It was revealed this time that he took the rocket's engine, which was a nuclear bomb. Tracking him to his underwater cavern hideout, Ben and the others realized he was stealing the rocket parts to repair a spaceship to return to his home planet in the Andromeda Galaxy. However, since he was going to use the nuclear bomb to trigger his launch and destroy Florida and thousands of people, Ben and the others had no choice but to stop him. With Gwen and Kevin trapped by Bivalvan's welding torch, Ben had to fight him on his own as Spidermonkey. However, Bivalvan still proved too much for him so he transformed Ultimate Spidermonkey who quickly defeated him.

Bivalvan then revealed that he and four others (P'andor, Andreas, Galapagus, and Ra'ad) were kidnapped by an alien called Aggregor before they escaped to Earth. Ben and the others left him behind while they took the bomb back to NASA, saying they would contact the Plumbers to ensure Bivalvan would get home. However, before the Plumbers arrived, Aggregor appeared, saying that no one escapes him. Bivalvan was then heard screaming off-screen.

Bivalvan reappears in Escape From Aggregor in Galapagus's flashback with lighter voice alongside Galapagus, P'andor, Ra'ad, and Andreas. During their time as prisoners, Bivalvan seemed not as violent but a leader of the five aliens while having a fierce rivalry with P'andor. He engineered an escape from their cell by using a device he had either assembled while in the cell or smuggled with upon being captured to unlock the cell door and neutralize the device Aggregor had used to nullify their elemental powers (Galapagus said "I'm following that guy", referring to Bivalvan). He also appears to have a natural ability to lead others and make the right decision, as shown on Aggregor's ship.

Upon realizing they weren't in a prison but on a spaceship, Bivalvan realized that they couldn't escape because there was nowhere to go. When Galapagus suggested using Aggregor's transmitter to call for help, Bivalvan approved of it, but P'andor opted to overthrow Aggregor and led Andreas in an attack on the bridge while Bivalvan, Ra'ad, and Galapagus went to the radio room. Unfortunately, P'andor and Andreas's attack alerted Aggregor to the escape of the others and they were all thrown back in their cell just as Galapagus's call alerted Magister Prior Gilhil. The Plumber Found them when they were in their cell only to be attacked by Aggregor. Bivalvan, P'andor, Andreas, and Ra'ad escaped, but Galapagus seemed to betray them in exchange for his own freedom. However, Galapagus revealed that he lied and incapacitated Aggregor and his robotic soldiers, impressing Bivalvan (who said "I'm following that guy"). The five aliens stole a shuttle and fled the ship only to have Aggregor shoot them down and cause them to crash on the planet they were flying by: Earth. Bivalvan opted to stay with the ship as it was their only way off the planet, but P'andor stated they needed to split up. P'andor, Andreas, Galapagus, and Ra'ad each went in separate directions while Bivalvan attempted to repair the shuttle through his raids at NASA.

At the end of Andreas’ Fault Bivalvan is seen in a stasis pod along with Galapagus, P'andor, and Andreas.

In Ultimate Aggregor, he was possessed to attack Ben's group, though after his headband was removed, he was confused about what happened to him & where he was before being warped back to his capsule. Kevin assumed Max had vaporized him, though he states that Aggregor had teleported him away. Bivalvan is successfully absorbed by Aggregor at the end of the episode.

As of the end of Absolute Power: Part 2, Bivalvan, as well as the other Andromeda Galaxy Aliens, are back to life after Kevin was turned back to normal.

Toys

 * Ben 10: Ultimate Alien 4 inch Alien Collection Water Hazard
 * Ben 10: Ultimate Alien 10 cm DNA Alien Water Hazard
 * Alien Creation Chamber Waterhazard

Trivia

 * Bivalvan's outer shell is strong enough to withstand Chromastone's attacks and P'andor's burn during the episode Escape From Aggregor. This would make him one of the more resilient aliens in Ben's collection. This is also proven in Map of Infinity, when Ben as Humungousaur angrily beat Aggregor, who successfully absorbed the Andromeda aliens. He stated that Bivalvan's armor allowed him to feel no pain.
 * Bivalvan's voice changes throughout the series. In Fame his tone was much deeper with a hint of a watery echo beneath. While in Escape From Aggregor it sounds younger, and the same voice used in that episode is seen again during Too Hot To Handle where Ben is merely using Bivalvan's form to calm P'andor down. Lastly, in Hero Time, when Ben uses becomes Water Hazard again the voice is deeper. This could have been a small mistake on the production teams' part for realizing that Water Hazard and Bivalvan needed separate tones in their voice, otherwise it would be confusing to tell the difference between them in later episodes.
 * His personality changes a bit when watching the episode Fame and Escape From Aggregor closely. At the time he was first introduced, Bivalvan was much colder and less patient to listen to Ben (though he should know of Ben's heroics). While in the flashback episode, detailing his escape, he had a calmer persona, albeit a little condescending towards those he found inferior or innocent. Perhaps Bivalvan's time on Earth and in prison made him more paranoid to trust others.
 * When Bivalvan uses a device of his to override Aggregor's prison lock and power disruptor, then later is seen on Earth, in Fame, effectively stealing parts from NASA imply that Bivalvan may have been a thief or skilled specialist of some sort before being kidnapped.
 * Bivalvan's name is a play on the word "Bivalve" meaning ' an organism(most likely a clam or an oyster) with two shells.
 * Considering Bivalvan's ability to shoot jets of water and control moisture, his name may also reference a water valve.
 * Bivalvan's name may also be a reference to the game development company "Valve" also his suit bears a resemblance to the HEV suit from the Half life series that is produced/developed/sponsored/owned by Valve.
 * Bivalvan may have been a law enforcer (police officer or millitary commander) on his home planet (since he had an electric device with him, said "Negative" instead of "No", and planned out how to get out of the ship[which failed due to the lack of cooperation of the others]).