Dog Man bought Flippy for free from Penelope's Pets and gave him to Chief for his birthday. Two other officers gave him a can of Supa Brain Dots. Chief put his can of Supa Brain Dots and Flippy into another room, where he ate one of his brain dots. After Chief left for lunch with the others and slammed the door closed, the can ofSupa Brain Dots toppled over and the brain dots fell into Flippy's tank, causing his brain to grow 11 times larger, giving him psychokinetic powers.
After discovering how his powers worked, Flippy cut out a hole in a paper bag, stole a purple trench coat and an orange, three-legged stool with black stripes from Chief to dress himself up as a human, becoming the Mysterious Stranger. However, he ends up looking more like a cat (Petey). He robbed Penelope's Pets, tied up Sarah Hatoff, Zuzu, and two Penelope's Pets workers, and then he stole a bunch of little plastic treasure chests, planning to get enough gold to purchase the biggest castle in the city. Fortunately, Zuzu chewed through the ropes and Sarah snaped a picture of the Mysterious Stranger. She thought he was Petey the Cat, because the orange-and-black-striped-stool looked like his tail and legs, and she posted it on her news blog. The news reached Petey at Cat Jail, and he gets enraged because he thought someone was walking around as him, so he escaped Cat Jail, using a Flat Petey (which Witch Doctor Boog. E. Feeva brought to life later in the story) as a distraction and built the Treasure Tank 2000 in his lab so he can catch his so-called "impostor".
Meanwhile, Flippy the Mysterious Stranger was still up to no good. However, he didn't know that the treasure chests he stole from Penelope's Pets were actually made out of plastic, until he tries to pay them at Kinney's real estate. The owner explained to him that treasure chests are made out of wood and filled with gold. Just then, both of them noticed on television that Petey the Cat on his Treasure Tank 2000 was hypnotizing people with his love ray to take everyone's money. The Mysterious Stranger decided to go and steal it, whereas the owner declined. The stranger grew mad and used his mind powers to send the owner flying away.
Dog Man shows up with Sarah, Zuzu, and Chief, just in time to see Petey, Flat Petey and the Mysterious Stranger (Flippy) arguing over the Treasure Tank 2000. Petey is chased back to Cat Jail as Flippy reveals who he is. As he was about to go and steal the Treasure Tank 2000, he realized too late that Flat Petey and the hypnotized Doctor Feeva had already escaped with it to the top of a snowy mountain while Flippy was speaking to Dog Man and the others. The evil fish chased Petey's paper clone out of rage, with Dog Man and everyone else following the villains to the top. Flippy freezes in his fish tank, but as Flat Petey sees Doctor Boog. E Feeva no longer useful and kicks him away, the doctor's belongings fall out of his bag. Flippy quickly reads one of the Witch Doctor's books and discovers how to live forever. Focusing his mind, Flippy's soul abandons his body and tries to possess Chief's body. Dog Man gets Flippy's soul in his mouth, and Flippy's soul slowly melts away until it was no more. His empty body is left to freeze on the mountain when Dog Man, Zuzu, Sarah, Chief and Boog. E Feeva use Flat Petey's frozen body to sled down the mountain.
Flippy's frozen body is recovered from the mountain by scientists to study his brain. He is rebuilt with metal parts and brought back to life with Living Spray, becoming Supa Mecha Flippy. He makes an army of Beastly Buildings and goes on an evil rampage in the city. Dog Man crushes all the Beastly Buildings with the help of Sarah, Zuzu, and Chief. Flippy becomes a good guy when Li'l Petey befriends him, and Flippy goes to Fish Jail for his crimes, but he and Li'l Petey make comics for each other and then he is happy.
Thanks to Li'l Petey's help, he got free from jail, and even aids them in fighting the Fair Fairy and the 22 tadpoles. He later became the 22 tadpoles' adoptive "father".
Flippy in this book was very overprotective, and was overwhelmed by the fact that tadpoles were making books about potty humor, gore, and death (in the quote mentioned: "There is nothing funny about poo-poo!"). He had to realize at some point that he may need to calm down a bit, and approaches the tadpoles saying that they can write what they wanna right about and he shouldn't be overreacting.
Trivia
Flippy was not meant to be angry, it was the GR-2 in the Supa Brain Dots that made him angry.
Although Flippy's brain grew 11× big, he wasn't always very smart at times, e.g. he mistook the plastic treasure chests from Penelope's Pets as actual treasure chests.
Flippy can be considered the central antagonist in Dog Man: Unleashed, as he appeared to be the only main threat in the first half, until Flat Petey shows up and becomes the true main antagonist of the book.
Despite Flippy not being the true villain of Dog Man: Unleashed, he was the one who started the trouble in the city and indirectly responsible for Petey's escape and Flat Petey's creation.
In Dog Man: The Musical, he is played by Crystal Sha'nae (Original) and Jasmine Smith and Princess Sasha Victome (North American Tour). Though he is played by a female, he is still referred to as a male, just like Li'l Petey.
Flippy makes a cameo appearance
In the first book, he makes a cameo on George and Harold's comics.
Like Dr. Scum, and the main antagonists from Super Diaper Baby and Ook and Gluk, he has triangular eyes, but unlike those other characters, he only has those eyes when he is angry, or when he was a villain. Nowadays, his eyes are usually circular.
