Carl, Trixie and Frankenbooger, better known as The Three Robo-Boogers are minor antagonists in Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy Part 1: The Night of the Nasty Nostril Nuggets, and the main antagonists of Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy Part 2: The Revenge of the Revenge of the Ridiculous Robo-Boogers.
Carl is a blob of snot with two bionic legs. He has bucked teeth
Trixie is bigger than Carl, and has many bionic arms. She lacks legs, and has stalks holding her eyes up.
Frankenbooger is the largest of the trio. He is a blob of snot with no legs, and two arms.
Nothing is known about their separate personalities, though they eat or destroy anything in their path. The Robo-Boogers also seem to care about one another, as Trixie and Frankenbooger sought vengeance upon Carl's death.
The Robo-Boogers are briefly seen at the end of Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy Part 1: The Night of the Nasty Nostril Nuggets. They are created by the remains of the Bionic Booger Boy, after Melvin is separated from the boogers and robotic body. They slid off of some walls and smashed the Combine-O-Tron. They then chase away the protagonists as the story ends.
Reign of Terror
The Robo-Boogers were beaten up and shot into space by Sulu the Bionic Hamster, who heard the screams of terror caused by the protagonists. The three are launched into space, but they later stowaway on a spaceship to get back to Earth, and attack the space station in the process. Later, George, Harold and Captain Underpants(who has lost his powers), have been pursued by the Robo-Boogers.
George, Harold and Captain Underpants learn that the Robo-Boogers' weakness is vitamin C when Carl falls apart after eating an orange. Before Trixie and Frankenbooger could eat George and Harold, Captain Underpants annoys them by dancing atop a toilet, and the remaining Robo-Boogers go after him. They the toilet seat, which has oranges under it, leading to orange juice splashing on them, killing the Robo-Boogers for good.