"By the Book" is the second segment of the twentieth episode of Star vs. the Forces of Evil. It premiered on September 12, 2016 alongside "Goblin Dogs", and is the second segment of the seventh episode in the second season.
Ludo is once again trying to understand his wand when he suddenly hears a voice from it that apparently only he can hear. The voice tells him to go after Star Butterfly and he complies with some reluctance. Meanwhile, Glossaryck is training Star to use her wand properly, but she is acting insolent and refuses to keep up. She claims that she does not need to train anymore and that she would rather stick to her narwhal blast, even though Glossaryck tells her that there are more spells she can learn. She finally gives up and takes Marco to have fun. When she accidentally refers to Glossaryck as not being her friend, he takes it personal and stuffs himself inside a donut box; refusing to get out or even talk to Star about anything.
Star and Marco take the donut box around with Glossaryck to the movies in an attempt to open up, but this only results in causing trouble with Star creating a mess with her magic (somewhat proving Glossaryck's point) and Glossaryck ruining the movie for the other patrons. They next try to set up a fake monster scenario, but Glossaryck sees right through it. Eventually, they decide to drop the donut box inside a garbage bin, but the bin gets taken out by a garbage truck. As they race to the truck to save Glossaryck, Ludo shows up with Spider and Eagle. Both Star and Ludo discover that they have each other's halves of the wand and try to fight, but their magic is pathetic. Marco also fights Spider and Eagle with mixed results.
During the fight, the donut box is crushed in the truck and as Ludo approaches Star, Glossaryck frees himself and calls upon the spell book. She has Star read from it and she manages to summon a warnicorn stampede to knock Ludo and his minions back through the portal. As Marco celebrates Star's success, Glossaryck claims that he was not hurt by Star's words and that he was pretending so that he can accurately assess the situation and have Star successfully defeat Ludo again. Despite it not making any sense, Marco accepts this explanation. As Ludo returns, with his minions, back to his lair, he happily tells the wand that "there's a book".
- The movie that Star, Marco and Glossaryck watch features a man being in a relationship with a Cthulhu-like creature (inaccurately called a squid by Glossaryck). This could be a parody of either The Little Mermaid or the Twilight Saga.
- Star and Ludo discover that they have each half of the star emblem.
- For unknown reasons, this episode (alongside "Goblin Dogs", which it is paired with) is missing from Disney+ in certain countries such as Singapore.
- October 6, 2016 (United Kingdom and Ireland)
- November 15, 2016 (Italy)
- December 13, 216 (Israel)
- December 18, 2016 (Japan)
- December 22, 2016 (Latin America)
- January 10, 2017 (Poland)
- January 13, 2017 (Southeast Asia)
- February 14, 2017 (Spain)
- October 3, 2017 (Portugal)
- February 24, 2018 (Philippines)