"Sophomore Slump" is the second segment of the forty-second episode of Star vs. the Forces of Evil. It premiered on November 8, 2017 alongside "Demoncism", and is the second segment of the seventh episode in the third season.
Marco decides to put in a full effort to living life in the present on Earth.
Three months after saving Mewni, Marco is relaxing at home in his cape he acquired. His mother Angie approaches him and tells him that going to Mewni has changed him, but not in a good way as all he talks about is his time there. She compares it to herself having gone to France and becoming the "croissant girl" due to how she insists on pronouncing it. While playing The Adventuring Zone with his friends, he continues to make remarks about Mewni that annoy Alfonzo and Ferguson, but amuses Janna. He speaks with Sensei Brantley who reveals that he gave himself a cape (a towel), but when Marco states that he earned his, he gets upset.
Later, Marco talks with Jackie-Lynn and tells her that he believes that everyone is jealous of him, but when she points out that he has never asked her about her summer, he realizes that he is the "croissant girl" and tells her that he will make it up to her. Marco shows up at Jackie-Lynn's house, apparently without his cape, and asks her out. They go to the Echo Creek Pier where they proceed to have fun together. When Marco presents $650, the pig out and spot some lobsters that are in tanks. They manage to rescue one of them and release it back into the sea.
As Marco and Jackie-Lynn hug, the latter realizes that the former is still wearing his cape underneath his clothes. She sits him down and tells him that she is "giving [him] an out". When he declares that she is his best friend, she tells him, "we both know that's not true" and leaves him for good. Marco decides to act as an exchange student for Mewni. As his friends and family see him off, Marco makes amends with Ferguson and Alfonzo, gives Brantley a cape of his own and gets his social security card back from Janna. He opens a portal and steps through; seeing Butterfly Castle in the distance.
- Adam McArthur as Marco Diaz
- Grey DeLisle as Jackie-Lynn Thomas
- Artt Butler as Mr. Diaz
- Nia Vardalos as Mrs. Diaz
- Nate Torrence as Ferguson O'durguson
- Matt Chapman as Alfonzo Dolittle
- Jeff Bennett as Principal Skeeves
- Abby Elliott as Janna Ordonia
- Nick Swardson as Sensei Brantley
- Jackie breaks up with Marco on good terms and they remain friends.
- Marco leaves Earth to stay on Mewni for a while.
- Jackie and Marco dated for almost 3 months.
- This is Jackie's only speaking role in Season 3.
- A painting at the restaurant is similar to Ariel and Flounder from Disney’s The Little Mermaid.
- Several posters in Jackie's bedroom allude to real-life bands and other media: