In a sleepy mountain town, Cindy's parents are murdered and her Christmas is stolen by a bloodthirsty green figure in a red Santa suit.
The Mean One is a Christmas horror parody. In a sleepy mountain town, Cindy's parents are murdered and her Christmas is stolen by a bloodthirsty green figure in a red Santa suit, The Mean One. But when the ravenous, Christmas-hating creature begins to terrorize the town and threatens to ruin the holiday, she finds a new purpose: trapping and killing the monster.
In Newville, on Christmas night, the mother of the girl Cindy is murdered trying to save her daughter from a trespasser. Nancy describes the man as a green monster dressed in costume of Santa Claus. Twenty years later, Cindy, who was hospitalized due to her mental illness, returns to Newville with her father during the Christmas holidays as part of her recovery from the childhood trauma. On arrival, they are stopped by Deputy Burke since Christmas ornaments are not allowed in town. They arrive at their house that is closed and start to decorate the house for Christmas. But during the night, the green monster kills her father at home. Nobody believes Nancy again but out of the blue, the local Doc Zeus tells her that the Grinch, a.k.a. the Mean One, killed his wife Martha twelve years ago, and nobody has also believed in his words and since then, he is chasing the Mean One in Christmas to kill it. Nancy visits Sheriff Hooper again, but he does not pay attention to her. Now Cindy decides to team up with Doc to kill the Mean One.—Claudio Carvalho, Rio de Janeiro, Brazil
During Christmas Eve in the town of Newville, a green humanoid creature dressed in a Santa Claus suit attempts to rob the Christmas decorations from the home of a young Cindy You-Know-Who. She stumbles upon the creature and gives him a necklace until her mother attempts to fight him. In the struggle, the creature accidentally pushes Cindy's mother against a nail that pierces her neck, killing her. Before the creature escapes, Cindy calls him a "monster".
Twenty years later, Cindy returns to Newville for closure and to spend Christmas with her father, Lou. She bonds with police officer Burke Goldman and reunites with Newville's sheriff Peter Hooper, who continues to dismiss Cindy's claim of her mother's murderer being a monster due to lack of evidence. He reveals that Newville stopped selling or putting up Christmas decorations after the incident. That night, Lou finds old Christmas decorations and puts them up with Cindy. While she is taking out the trash, the creature locks her out and kills Lou before stealing their decorations.
While at the hospital, Cindy meets Newville's mayor Margie McBean, who is uncomfortable with Cindy's claims of the creature, believing it will cause panic. After her father's funeral, Cindy finds a rare flower in her home and traces it to a mountain via a website. Cindy finds the wallet of a missing person and sees the creature killing a couple before retreating. Shortly after, Hooper tells Cindy he cannot investigate as the mountain is in federal territory, although Burke agrees to help. Meanwhile, the creature slaughters a group of Santa cosplayers in a local bar.
As the creature attempts to break into Cindy's home, he is scared off by a man known as Doc Zeuss, who believes Cindy's story since his wife was murdered by the creature years ago. Burke goes to the mountain and finds the creature's hideout with several wallets of missing people. Cindy trains and prepares to kill the creature, who rampages through Newville and kills several residents. Burke discourages Cindy from facing the creature and finds out the wallets all belonged to tourists who were lured to the mountain by the same website Cindy saw, which is owned by Mayor McBean. He confronts Hooper, who confirms the creature's existence and explains that after Cindy's mother's death, the creature returned every Christmas to slaughter more people, and later his hideout was found. Hooper and Mayor McBean collaborated to make the website and send unsuspecting tourists to sacrifices in order to stop the creature's killing spree in addition to removing all Christmas decorations from the town.
Mayor McBean attempts to leave the town, but the creature kills her on the way. Burke heads to the mountain to kill the creature but becomes injured and is rescued by Cindy, Hooper, and Doc. Hooper goes after the creature but is killed. Cindy retreats to her decorated home and waits for the creature. When the creature arrives, she ambushes and engages him in a fight. Cindy finally incapacitates the creature, but before she can kill him, Cindy sees that he is still wearing the necklace she gave him twenty years ago. Cindy realizes her mother's death was unintentional, and the creature never wanted to hurt anyone; his murderous behavior sparked when she called him a "monster", so she forgives him and kisses the creature on the cheek. This act of kindness causes the creature's heart to grow three sizes, which ends up exploding and kills him.
Sometime after, Newville reverts to displaying Christmas ornaments, the creature is deemed an urban legend and causes the town to become a popular tourist destination; Cindy and Burke start a romantic relationship and the narrator hints that the creature may return next year as his growl is heard.
