Scooby-Doo and the Ghoul School

Scooby accidentally swallowed the remote control that the Calloway cadets used to rig the volleyball. The cadets had hidden a remote inside the ball to control its movement and cheat during the game. When Scooby grabbed the ball, he inadvertently swallowed the remote, which disabled the cadets' control and allowed the Grimwood Girls to win the match fairly.

The cheating incident earlier creates tension between the cadets and the girls, foreshadowing the later conflict.

Revolta is a power-hungry witch who plots to kidnap the Grimwood Girls and enslave them to increase her own magical power. She uses her minion Grim Creeper to help execute her plan, which involves capturing the girls during a field trip and casting a potion at midnight that would turn them evil and obedient to her will.

Revolta uses her magical powers to hypnotize Shaggy during the time before the field trip. This allows her to manipulate him into leading the Grimwood Girls into the dangerous Barren Bog, where Revolta's plan to capture them can be carried out. The hypnosis gives her control over Shaggy's actions without his conscious awareness.

Shaggy's strange behavior during the lead-up to the field trip hints at the magical influence over him.

During the field trip to the Barren Bog, Revolta's spider-bats begin systematically capturing the Grimwood Girls one by one. Meanwhile, the Calloway cadets fall into quicksand and must be rescued by Elsa and Tanis, proving the girls' resourcefulness. Revolta uses this distraction to advance her kidnapping plan and complete her evil potion that will turn the girls at midnight.

Matches is left behind at the school, foreshadowing the danger of underestimating Revolta's reach.

As Revolta administers the potion through hairdryers at midnight to turn the girls evil, Scooby and Shaggy inadvertently interrupt the process and reverse the potion's effects. Elsa then throws Revolta's magical wand into the potion, causing a spectacular explosion that destroys the potion entirely, thwarts Revolta's plan, and frees any remaining captives.

The students are daughters of famous monsters: Sibella Dracula (daughter of Count Dracula), Elsa Frankensteen (daughter of Frankenstein Senior), Winnie Werewolf (daughter of the Wolfman), Phantasma (daughter of a phantom), and Tanis the Mummy (daughter of an ancient Egyptian mummy). The school provides a safe haven for these monster daughters to learn and develop their abilities.

After the potion explodes and Revolta's plan is thwarted, the Calloway cadets arrive in a pedal-powered helicopter just in time to rescue everyone from the exterior of the castle. Their arrival signifies the reversal of their earlier antagonism toward the girls and demonstrates the friendships formed during the crisis.

Matches is a tiny dragon who serves as a protective companion to the Grimwood Girls at the school. He provides comic relief while also acting as a loyal guardian. During the final confrontation, Matches joins Scooby, Shaggy, and Scrappy in their mission to rescue the captured girls from Revolta's castle.

Revolta wants to enslave the Grimwood Girls to increase her own magical power. By capturing daughters of powerful paranormal families, she plans to use their inherent magical abilities to strengthen herself and create a fortress of darkness where her magic would be supreme.

Inside Revolta's castle, the heroes face a shape-shifting Mirror Monster that can mimic the bad versions of anyone who gazes into its mirror. This creates a psychological challenge where the heroes must resist seeing their negative reflections, which the monster uses as a weapon against them.

The Calloway cadets are initially competitive and somewhat hostile toward the Grimwood Girls, cheating during the volleyball match to ensure victory. Their father Colonel Calloway arrives at the Halloween open house with a protective but dominating demeanor. This initial tension sets up their character arc as they eventually become heroes who rescue everyone, demonstrating growth from rivals to allies.