A two-hour television film called The Battle for Mewni,[8] which comprises the first four episodes of the third season upon being re-aired, premiered on July 15, 2017.
As Marco tries to fashion something to fight them off, he recounts how he tried to cheer up Star because she left her phone number for her crush, a keytar-playing student named Oskar, but he has not called her back.
They discover that Pony Head has been brainwashed to be a compliant princess and try to evade the robot guards and the reform school's headmistress Miss Heinous.
While trying to evade the police, Star encounters a woman by the river bank named Brigid who likes making things out of discarded hair and taking care of injured animals.
Missing her family and friends, she returns to a very worried Marco and turns herself in to the police who have her wash the other squad cars as part of her police-supervised community service.
They start to become friends on the way there after learning they both like Mackie Hands and a band called Love Sentence, but when Marco wants to leave to catch the marathon, Tom refuses to let him go, and gets angry, voiding his chance to earn an anger management graduation badge.
However, as Baby turns to leave, the apple Star failed to levitate suddenly grows into a tree, causing her to change her mind and pass her.
Later, Baby reports to Moon that, despite her faults, Star's magic potential is far above what hers was at her age, adding that it might be comparable with the ancient queen Eclipsa.
Marco borrows Star's Dimensional Scissors to find a place to walk the laser puppies, but he soon becomes accustomed to its conveniences, opening a bunch of portals from his bed to access things.
Pony Head tells Star the bad news that the Bounce Lounge, their favorite partying venue, is closing.
Marco gathers video evidence of Jeremy's shenanigans, and is about to share it with Sensei on the day of the demonstration, but realizing it isn't honorable, he apologizes.
Star and Jackie start bonding from wearing similar t-shirts and riding skateboards to the concert where they stop and help an animal in the creek.
Meanwhile, Moon visits Ludo's parents and with help from his brother, Dennis, learns that he is at the monster temple and in possession of the other half of Star's wand.
Since Toffee is immortal, Moon approaches Eclipsa, who is revealed to have been held in suspended animation inside a crystal prison for 300 years, to learn a dark magic that can destroy him.
A jittery Pony Head confides to Star that Tom is undergoing a "demoncism", which is meant to turn him into a more normal, tamed being.
They secretly infiltrate the ceremony for Star to rescue Tom, but the demoncism goes ahead as scheduled, only for its organizer to reveal that he still has plenty of rage in him.
Star and Marco discuss how their relationship has been since she confessed that she had a crush on him before finally taking a sincere photo that ultimately leads to them kissing, leaving them both flabbergasted and dumbstruck.
Under her rule, the living conditions of the monster population have greatly improved and she has invested a huge amount of resources into unsuccessfully freeing Globgor from his imprisonment.
Marco and Kelly defeat her and her assistants easily with their combined teamwork and depart together as "breakup buddies" holding hands.
When Ludo hears Star's Wand is now in Eclipsa's possession, he finally snaps as he begins scheming on stealing it and openly tells Dennis he hates the castle.
Realizing how much his brother has done for him, Ludo steals the deed to the castle and continues the reconstruction with Dennis and their other siblings, allowing him to finally abandon his villainous ways.
Unfortunately, they go back too far and end up meeting the first Mewmen settlers of Mewni, who Glossaryck gifts the Royal Magic Wand to help them defend themselves and survive.
Eclipsa reveals that she has successfully restored the Book of Spells and found a way to free Globgor from his crystal prison, but they ultimately decide not to do it as the Mewmans are not ready to accept him yet.
However, Eclipsa displays indifference to how her people view her and argues that they have not even given her a proper coronation, causing Star to decide to give her one.
With Eclipsa and Globgor now ruling Mewni peacefully, Star announces her plans to travel abroad with Tom while Marco and Janna decide to return to Earth.
While happy at first, Tom begins to suspect that Star is stalling, especially when she starts saying goodbye to people he has never met like Doop-Doop, her very first spell which she left abandoned in a shed.
Sensei and Oskar are shown to have become employees at the restaurant, which Janna has been banned from, while Principal Skeeves and Mr. Crandle show no ill will towards Marco, who earned his high school diploma early.
She backs down at the last minute and she and Marco decide to fight Wyscan when he proves immune to Star and Meteora's magical powers.
As Mina resolves to fulfill her oath to Queen Solaria to wipe out all monsters, Moon reveals she sided with her to prevent her from making matters worse and that she blames Eclipsa for everything that happened to her since the events of "Tough Love".
Fortunately, River manages to sneak away with Globgor while Hekapoo, who snuck away from the other Magic High Commission members, rescues Star, Marco, Moon, Eclipsa and Meteora.