Mon Mon Mon Monsters

Lin Shuwei is a meek, straight-A student with no friends who is framed for stealing the class funds and humiliated by a gang of bullies. The group, led by Renhao and including Wu Sihua, Liao Kuoheng, and Yeh Weichu, spreads the shame across the school. Lin secretly records part of the encounter on his phone, hoping for proof, but the humiliation continues.

Lin confronts the bullies at their make-shift hideout in the maintenance room of the school's abandoned swimming pool. Renhao mockingly confesses to the crime, while Sihua frames Lin further by staging a perverse act and taking photos. Lin's phone records the confrontation, capturing essential evidence.

Ms. Lee, a devout Buddhist teacher, proposes a grim solution: Lin should take the blame and the three male bullies will work with him, under the pretense of making the four of them 'popular'. She assigns them to do community service so that the four boys are kept close.

The four begin community service at an elderly home, feeding residents. The bullies abuse the elders, painting faces and forcing them to fight as part of a cruel game, while Lin initially participates but gradually feels drawn into the group.

That night they find a locked box at the elderly home and plan to return to break it open. While leaving, they encounter a pair of flesh-eating ghouls living in the building's elevator shaft; a younger ghoul is struck by a car and carried back to their hideout.

Back at the maintenance room, the younger ghoul reawakens, showing regenerative powers and the ability to climb walls. The bullies restrain her, chaining her to a pillar and sealing her mouth with a plate.

Lin begins researching the ghouls, identifying the younger one as Lee Shiu Jen, who disappeared in 1985 alongside her sister, known as the Voodoo Master. He uncovers their brutal history and learns that the ghouls were once human.

Renhao and the others extract samples from the captive ghoul and study them in the school lab, noting the lack of red blood cells and the presence of spores. They observe that contact with normal blood causes the blackened cells to spread, and that sunlight can cause the cells to combust.

A prank on Lin leads Renhao to violently attack him in front of the class, prompting Ms. Lee to intervene. The bullies escalate and poison Ms. Lee’s drink with the monster’s blood, increasing their cruelty and detachment.

Ms. Lee becomes severely ill and dies after a basketball game, bleeding black and combusting upon sun exposure. News footage of the incident circulates, and the elder ghoul notices the school uniform on screen, hinting at the broader threat.

The elder ghoul hunts students wearing the school uniform, ambushing a student at a vending machine and later slaughtering a bus full of students. Sihua is on the bus and manages to photograph the monster, but she is killed in the attack.

The remaining bullies decide to lock both ghouls in the maintenance room and douse them with gasoline to burn them alive. Lin sabotages the plan by enabling an escape, determined to do one thing right in his life and avoid becoming like his tormentors.

Under the rising sun, the younger ghoul burns as the elder sister shields her, and the two die in each other’s arms. Lin leaves the maintenance room, having witnessed the sisters' final moments.

Later, Lin is assigned to lunch duty and continues to be tormented by his peers. He poisons the rest of the class’s soup with the monster’s blood and then stands up to scream as he combusts, with his classmates burning in the background.