Scrappy Doo is the hidden main antagonist of the live-action Scooby-Doo film. He is Scooby's nephew.
Beginnings[]
Introduced in 1979, Scrappy ranks with the likes of Jar Jar Binks as one of the most hated fictional characters ever. He was extremely obnoxious and annoying, he effectively replaced Fred, Velma, and Daphne on the show, and the cartoons he was in had actual monsters who were dealt with in a generic slapstick manner and whose existence wasn't even acknowledged as unusual. Because of this, Scrappy became the villain of the live-action Scooby-Doo film, after about 15 years of absence from the franchise and never appearing again afterwards.
The film[]
During a flashback recalled by Velma at one point in the film, Scrappy is seen bothering the gang in the Mystery Machine, bragging about how he will fight ghosts and monsters. Fred tells him he has told him "Scrappy for the thousandth time there is no such thing as ghosts." Scrappy argues that ghosts do exist and when he finds them, he will give them a dose of "puppy power" and he then urinates on Daphne. When Scrappy realizes this, he gasps in shock and Fred immediately stops the Mystery Machine, sending Scrappy flying into the windscreen.
As he slides off, Fred scolds him for urinating on Daphne. After fixing himself, Scrappy crosses his arms and irritably insists it was an accident, but Fred tells him he was marking his territory. Now realizing that Fred is protective of Daphne since he is the leader, Scrappy angrily tells him he isn't worthy of being the team leader. He orders the gang to listen and announces it is time to appoint him as their "unquestioned" leader or else he'll leave. Scrappy is then unceremoniously thrown out of the van in the middle of the desert along with his suitcase, with no one giving a second thought.
The puppy hollers out to them they can't do that since people adore him (which is not exactly true). He then kicks his suitcase in anger and frustration, knocking it over and hurting his foot. Scrappy says he's as cute as "a Powerpuff Girl" and that he'll get his own TV show as he sits on his suitcase, alone and friendless.
Several years later, Scrappy disguised himself as Emile Mondavarious, the owner of Spooky Island, though the gang didn't know. He had teamed up with an insane man named N'goo and his evil cohort Zarkos. Scrappy and his allies created an army of monstrous demons through voodoo, but the monsters die when exposed to sunlight, so they possessed humans to become immune to sunlight while the souls of the people were converted into protoplasm and kept in the cave beneath the island. By absorbing the souls, Scrappy is able to become a powerful monster known as Scrappy Rex.
He only needed Scooby's protoplasm (a "pure soul") to complete his transformation and become unstoppable. He then chased Scooby and Shaggy until he had them cornered. He then managed to catch Scooby after Mary Jane hands him over. Scooby tells Scrappy to sit down and punches his nose, making Scrappy roar angrily in his face and take him over to the Pinscher to extract his protoplasm. But Zarkos falls over the vat after his fight with Daphne (who pushed him in), releasing the people's protoplasm. Scrappy tells the Mystery, Inc. gang their fight isn't over and he'll still kill them, but Shaggy gets Scrappy's attention by calling him a bad puppy and he finally defeats Scrappy Rex by pulling the Daemon Ritus out of his chest and destroying them. While screaming in terror and horror, he loses all of his protoplasm and then morphs back into Scrappy-Doo. Scrappy faces his uncle, telling him he can still take him and he challenges him to a rematch, but Scooby easily whacks Scrappy into a wall. In response, Scrappy says, "Is that all you got?" and Scooby shrugs.
Scrappy and his henchmen are then taken to prison when the police helicopters arrived on the scene, with Scrappy being taken away in a dog cage. His last words to the gang are, "And I would have gotten away with it, too! If not for you meddling sons of--", only to be cut off by a police officer shutting the door as the puppy continues to rant and rave. The gang are in shock over Scrappy almost saying the bad word (also wondering where he heard it), but the subject is immediately changed with the news people talking to the gang again.
It is currently unknown what happened to Scrappy and his henchmen in the end, but they most likely remained in prison.
Personality[]
Scrappy was characterized by extreme arrogance and egomania, believing he could overpower any opponents with his "puppy power". He was also disrespectful towards the gang and frequently mocked them, calling them "losers" (and later, even trying to call them "meddling sons of--", but was cut off before he could finish). His insistence that ghosts were real, coupled with his obnoxious behavior, annoyed Mystery, Inc. to no end, culminating with Scrappy arrogantly demanding that they appoint him their "unquestioned" leader or else he would leave, foolishly believing that they valued his company, when in reality, they would gladly take the chance to get rid of him. This led to his abandonment, which would cause his downward spiral into outright villainy.
As a villain, following his corruption by the Daemon Ritus, Scrappy showed no problem with committing murder and kidnapping and was perfectly happy to consume the souls of thousands (perhaps millions) of innocent people in order to increase his own power, kill Mystery, Inc., and rule the world with his army of monsters. Upon assuming the form of Scrappy Rex, he became even more brutal and arrogant, and even after his defeat, he still insisted he could fight the gang, only to be quickly overpowered (though his ego was not damaged in the slightest).
The Scrappy from the cartoons was also tough-acting and overconfident, though not as obnoxious and to a much lesser extent, and was also more analytical and intelligent, sometimes proving to be an even better sleuth than most of the gang, with the possible exception of Velma. He also idolized Scooby and was firmly loyal to the group, often courageously (or brazenly) standing up for them when they were being attacked. How Scrappy went from cocky but heroic to obnoxious and demanding (then villainous and cruel) is unknown, though perhaps in the cartoons, he never became a villain and / or something terrible happened to him — or was caused by him, inadvertently or otherwise — that caused the gang to stop talking about him.