Return to Mewni
Marco's parents try to console Marco. Star and Queen Butterfly take the Magical High Commission members to the sanctuary, but their carriage breaks down because of the fritz. Some of Ludo's rats try to take away the members while they are camping, but they fight them off. They make it to the sanctuary, but the well spring that is supposed to revive the members is corrupted with dark magic. Queen Butterfly and Star rest and think about what to do next: Queen wants them to stay and hide, but Star wants to fight.
Moon the Undaunted
Queen Moon shares her story of when she was a teenager and her mother had died. She had to decide between signing a peace treaty or going to war against the lizards. She partly melts the ice encasing Eclipsa, to learn some dark magic from the forbidden section of the Book of Spells. She confronts Toffee and uses the dark magic to sever his finger, which he is unable to regenerate and then flees.
Book Be Gone
Ludo finds that his wand is now embedded into his hand. He finds Glossaryck, who tells them that the Magic High Commission has been defeated. Ludo wants to celebrate by writing his story into the Book of Spells, but the book will not let him, as he is not the owner of the book anymore. Despite multiple attempts, he is unable to write into the book until he throws the book into the fire, at which it burns up.
Marco and the King
King River tries to take care of the kingdom by partying it up every day, but he and his subjects wear down quickly. Marco arrives, but the King has to deal with angry villagers as well as a large monster who approaches the castle, destroying everything in her path. River tries to hide, but Marco encourages him to stand up to the monster.
With the sanctuary all sludged up, Star and her mom flee and find a new hiding place at Buff Frog's. Star wants to sneak out to fight, so she gets Buff Frog to distract her mom with some Mewnian board games such as Puddle Defender, which Buff and Moon find have a biased perspective towards the monsters instead of the Mewnians. However, Buff Frog later sides with Queen Butterfly and forbids Star from leaving. Buff's youngest tadpole Katrina is able to sneak Star out.
Ludo has taken over the kingdom, and has imprisoned Marco and River, but he finds that he is not popular at all among the kingdom's villagers. He tells River to make him popular or else he will levitate him into the sky. Marco uses a stick of butter that Ludo left to free himself, but River has eaten his part of the butter so Marco has to steal Ludo's key. He meets with some of the court entertainers, and they steal the key, but River refuses to escape. Ludo levitates River into the skies while Marco and the entertainers conspire what to do next.
Star attacks Ludo at the castle but Ludo suddenly stops when he gets a signal from his hand. Star tells Ludo that Toffee is controlling him, but Spider is able to capture her in the meantime. Marco breaks her out and calls the entertainers but Ludo arrives and imprisons them except for Star. Ludo asks Star about his wand hand. While Queen Moon and Buff Frog break Marco out, Star agrees to use the whispering spell to free the magic in the wand and there is a big blast. Star finds herself in a sea of dark magic inside Ludo's body, and Ludo is taken over by Toffee again. Queen Moon agrees to return Toffee's finger in exchange for Star's freedom. Toffee resurrects, but tells them that Star is gone. But as he leaves, Star is able to find her magic and come out to Mewni. She defeats Toffee with a magical blast from her restored wand; Ludo drops a pillar on Toffee to finish him off. Ludo asks Star to send him back to the void so he can find himself some more. While King River returns on some eagles, Queen Moon checks on Eclipsa who is still encased in crystal, however as Moon leaves, the crystal that holds Eclipsa cracks.
- Eden Sher as Star Butterfly
- Adam McArthur as Marco Diaz
- Michael C. Hall as Toffee
- Alan Tudyk as Ludo/River Butterfly
- Sonny Ashbourne Serkis as Young River
- Artt Butler as Mr. Diaz
- Nia Vardalos as Mrs. Diaz
- Grey DeLisle as Moon Butterfly
- Katie Driver as Young Moon
- Amy Sedaris as Mina Loveberry
- Zosia Mamet as Hekapoo
- Kevin Michael Richardson as Rhombulus
- Fred Tatasciore as Buff Frog
- Esmé Bianco as Eclipsa Butterfly
- Natalie Palamides as Foolduke
- Patrick Stump as Ruberiot
- Jeffrey Tambor as Glossaryck
- This is the first animated movie to premiere on Disney XD (unless one counts the movie version of the Gravity Falls series finale, "Weirdmageddon").
- The titles for the individual episodes are as followed:
- "Return to Mewni/Moon the Undaunted"
- "Book Be Gone/Marco and the King"
- "Puddle Defender/King Ludo"
- The missing part of Star's wand is re-merged in "Toffee" and takes on a third new appearance.
- Eclipsa Butterfly speaks for the first time in the series.