"Princess Quasar Caterpillar and the Magic Bell" is the first segment of the sixty-fifth episode of Star vs. the Forces of Evil. It premiered on April 7, 2019 alongside "Ghost of Butterfly Castle", and is the first segment of the ninth episode in the fourth season.
Ludo becomes determined to figure out how to not let his past hinder him any longer and continue on with the rest of his life.
In a bizarre repeat of "Bon Bon the Birthday Clown", Princess Quasar Caterpillar and her friend Hanna are waiting in a cemetery for the return of Nob Nob the Birthday Clown when their friend Shmarmo and his girlfriend Shackie arrive. Nob Nob turns out to be Ludo who is posing as the clown along with his sidekicks Fish and Crab. He demands that Quasar give him her "wand", but remembers that she has a bell instead. He is instantly defeated and sent through the portal back to his home where he is reunited with Dennis, Eagle and Spider. Dennis tells Ludo that he finally moved out of his parents house and that he has something he wants to show Ludo. Ludo is reluctant, but goes along and discovers that Dennis spent his life savings on buying the castle back, which worries Ludo as he has been relapsing into his old ways and has been wanting to change. To make matters worse, Dennis rehired his monster minions who are happy to be back.
As the castle is getting rebuilt, the Monsters ask Ludo about what his plans are, but he does not want to think about it. The Monsters begin to deduce that Ludo is plotting some way to get the wand back which is now in possession of Eclipsa. Half the minions think he will marry Eclipsa to get it while the other half think he will take it by force and begin arguing. Ludo gets upset and tells them that he would use them as a distraction and incapacitate Eclipsa while she slept. Dennis comes back and gets upset about Ludo plotting again when they are approached by Evil J. LandBaron who reveals that Dennis signed away all of the Avarius family fortune as well as the castle to him. As LandBaron laughs at his win, Dennis is defeated for losing everything and thinking that Ludo no longer cares.
Ludo, feeling regret for his actions, dons his old villain outfit and reunites with Spider and Eagle and breaks into LandBaron's house. Still using the term "wand", he sets his two minions onto LandBaron who, presumably, devour him. Later, Ludo surprises Dennis by revealing that the got the rest of their siblings (Yudo, Dudo, Kudo, Mudo, Tudo, Fudo, Zudo and Menudo) to come and help rebuild the castle for them. Ludo, having apparently overcome his addiction, reveals that he also built a basketball court and has himself and Dennis play together on it with the score mark sign labeled "Ludo vs. The Forces of Evil", implying that he has completely turned over a new leaf.
- Jeff Bennett as Bearicorn, Giraffe Monster
- Dominic Bisignano as Shmarmo, Lobster, Spikeballs
- Nika Futterman as Hanna
- Mark Gagliardi as Man Arm
- Adam McArthur as Big Chicken
- Daron Nefcy as Skackie
- Fred Tatasciore as Evil J. LandBaron III
- Bresha Webb as Indexia
- The people in Quasar Caterpillar's dimension are doppelgangers of people from Earth and Mewni:
- The beginning of the episode is almost identical to the events of "Bon Bon the Birthday Clown".
- Like "Ludo in the Wild", this episode briefly features Frédéric Chopin's Nocturne in E-flat major, Op. 9, No. 2.
- The basketball scoreboard at the end of the episode reads "Ludo vs. the Forces of Evil", referencing the very title of the series.
- June 7, 2019 (Southeast Asia)