Meteora comes back with a vengeance, sucking the souls of everyone but Marco and Tom, the former of whom sacrifices himself to give Tom time to find Star, sending him away by telling him about his kiss with her scandal! Marco releases them from the booth by finally taking sincere photos which ultimately lead to him kissing Star, leaving them both flabbergasted and dumbstruck. Outraged by the Commissions lies and the fact that they are not the true royal family, Star sets Eclipsa free and runs off. She has to take care of the dog and find its owner. Marco meets Jackie again but the Naysaya starts to act up, so Marco decides to spill out all his insecurities in front of Jackie in an impassionate monologue. C r andle show no ill will towards Marco, who earned his high school diploma early. They find a well that Star remembers she came out of with Moon and realize that this is their way into Mewni.
Despite this, however, Moon still can not get herself to trust Eclipsa and decides to leave with River, choosing not to oppose her rule out of respect for Star's decision to cede the throne to her. However, the game reveals they are lying and punish them until they reveal the truth: Eclipsa's Mewman husband had her replaced with Festivia, who was actually a peasant. They fight and just as Star is about to be defeated Eclipsa takes her wand and regresses Meteora into a baby. As everyone's souls return, Star allows Eclipsa to keep her wand as she believes it should be hers. Meanwhile, Star and Marco tend to the pig goats to talk and the two finally admit their feelings, followed by a kiss. In the same month, the series was renewed for a fourth season.
Nonetheless, Eclipsa hands the kingdom back to Moon after she promises stop the army and to let her and her family go. When Star and Jackie start having fun together, Marco starts to feel jealous and wants them to go on without him, but Jackie convinces him otherwise. He easily defeats them due to his long-time training in the Neverzone, but assures them that he already is a knight in his own right. Pony Head finds the concept boring and tags along with Marco to pick up a pizza from Emilio's shop. The two families compete in Flags, a king of the hill game where whoever plants their flag atop a dangerous hill full of obstacles gets to look down on the rival family members for a year. Though her father does little to actually help, Star does eventually get help from a romantic interest once again, just like her mother in the form of Marco. Spider senses something in one portal, so Dennis ventures into it and finds Ludo having a mental breakdown in a makeshift home with their parents made up of various objects to keep himself company.
Buff Frog refuses and escapes with Meat Fork. Eclipsa reveals that she knew that Moon planned Globgor's escape at her coronation and suggests that they either wait out Mewni's destruction or go back and fight. After Moon accidentally trips the archive's alarm, they quickly return to the castle, only to run into Star. Upon retrieving her ledger, Moon finds that what has been haunting the castle all along was actually Mina Loveberry. Although calm and well-meaning after being released from crystallization, Queen Moon and the High Commission try to keep Star far away from her as possible. Marco turns to Glossaryck, a genie inside Star's book of magic, for advice on how to stop her. Star ends up going into town by herself where she confuses a pirate-themed restaurant for having real pirates and trashes the place.
Meanwhile, Marco's karate instructor wants his students to channel their emotions to walk across hot coals. They are rescued by Foolduke and Ruberiot, who reveal the pie recipe they thought was Moon's has been with the Pie Folk for generations. However, the box reveals they are lying and force them to tell the truth: Eclipsa's ex-husband, King Shastacan, had her replaced with Festivia, who was actually a peasant. Upon discovering he is secretly hiding the cape King River gave to him on Mewni under his hoodie, she tells him that he's only staying in Echo Creek to make her happy for her sake. However, Star convinces her to stop by pointing out that she will just prove herself to be the villain everyone claims her to be.
Ludo's minion Buff Frog infiltrates the reenactment as one of the monsters to try to steal the wand. Pony Head eventually snaps out of her depression after her favority drama manages to get a happy ending. Olga's to rebel and to kick Heinous out, leaving her living out of a car. Just as Meteora was about to win, Eclipsa declares her love for her daughter, distracting her long enough for Moon to reverse the situation. Afterwards, Marco decides he wants to return to Mewni as an exchange student.
Star returns to the Diaz family where she meets Marco's newborn younger sister. See you all next season! Believing they have come to retake the school, the princesses fight them but are defeated, with Meteora taking Pony Head's horn. Having completed her lesson, Meteora and Glossaryck travel back to the present, with neither Janna nor Eclipsa having noticed they were ever gone. The first season took two years to make and consists of thirteen episodes. She defeats Toffee with a magical blast from her restored wand; Ludo drops a pillar on Toffee to finish him off. Although Marco thinks it's much like the , Star's is more extreme. The Diaz parents are hoping this can get settled so that they can have dinner with the Morrisons.
Due to her amnesia, Moon initially opts to stay with the Pies, until she regains some of her memories after she and Star sing together. While there, the group catch up with many of their friends. They are then seen holding hands, much to Pony Head's dismay. Marco confronts Star about Ruberiot's claim that she has a crush on him, causing her to run off. They soon discover in the palace's underground chamber that Mina Loveberry has been camping out capturing unsuspecting monsters to keep order.