Manny Armstrong is a Plumber's kid introduced in Ben 10: Alien Force.
Manny was actually born as a human who was taken to the Null Void by Servantis. He used Kevin's powers and a Tetramand to create Manny's actual form. He, along with Helen, Alan and Pierce formed a group, namedAmalgam Kids, and they were used by Servantis to do "nasty things". After they failed in their ultimate mission - destroy Ben Tennyson - their memories were wiped by Servantis.
Years later, Manny became part of a team of young Plumbers apprentices, the Plumbers' Helpers, which included him, Helen and Pierce. However, they had little knowledge of the technology they used, and Pierce was sucked by a Null Void Projector they had confused with a disintegrator weapon. Believing that Pierce was dead, Helen and Manny continued the work, capturing many kinds of aliens they confused for criminals and sending them into the Null Void. Though part of those they captured were DNAlien, most of them were just innocent aliens.
In Plumbers' Helpers, they eventually encountered Ben, Gwen, and Kevin. Despite Helen's doubts, Manny immediately assumed they were DNAliens, and they captured Kevin in order to interrogate him, then send him in the Null Void. However, Ben and Gwen came to free Kevin and were eventually able to explain to them the truth. After learning the error of their ways, Helen and Manny travel into the Null Void to look for those they've wrongly imprisoned.
In Voided, Manny is one of the resistance fighters under the orders of The Wrench battling D'Void. A past battle cost him his lower left hand, which has been fitted with a crude clamp replacement.
Manny returns from the Null Void in War of the Worlds: Part 1 and War of the Worlds: Part 2 and helps Ben and the others fight off the Highbreed. In the end, he becomes, along with Alan, Cooper, and the other Plumber's helpers, a pupil of Max.
Manny appears again in Vengeance of Vilgax: Part 1, where he, along with Max's other pupils, tried to defeat Vilgax, but Manny was easily defeated and threw onto a tree.
In Above and Beyond, the Plumber's helpers came on a satellite in order to save Max from a seemingly brainwashed Ben. Manny was the more willing to fight Ben, but, when he eventually found him, was easily defeated by Rath. During their fight, they accidentally damaged the gyroscope, causing the satellite to start falling towards London. By working as a team, the helpers were able to neutralize Humungousaur and throw him into space. They then tried to sacrifice themselves to prevent the crash, but didn't need to, as it was revealed all of this was just a test to see if they were worth being true Plumbers, except the falling part.
In Absolute Power: Part 1, Alan informed the team that Ultimate Kevin had stolen Manny's powers. However, he got his powers back when Ultimate Kevin was returned back to normal.
He returned in Weapon XI: Part 1, when he and Helen were on Khoros taking Gorvan into custody. However, they were attacked by Phil and Leander. Fortunately, Ben, Gwen and Rook arrived just in time and saved them. Ben took them to Kevin's garage where Alan explained that they were used by the Rooters and had their memories wiped. When he came to the Null Void to help Kevin, he, Helen and Alan were brainwashed byServantis and were commanded to destroy Ben. In the battle, he defeated Rook but was quickly defeated byAlien X who was controlling Leander's body. At the end of the episode he, along with the others joined the Rooters and was commanded to hunt down Ben.
In Weapon XI: Part 2, just as they were about to destroy Ben, a mutated Kevin grabbed Servantis, destroyed the crystal on his forehead and used Feedback's powers to free them from his control forever. He and the other Amalgam kids then returned to Earth.
- According to Dwayne, Manny's mother was a Tetramand, but she died when Manny was still a baby. This, however has never been stated on-screen.
- In the episode The Rooters of All Evil, this has been retconned.
- In the episode Weapon XI: Part 1, Manny is now a full pledged Plumber, and the lower right hand that he lost is now restored, or replaced.