Ghosts provides examples of:
- Arc Words: "Just go with it!"
- Bait-and-Switch: Upon returning home from the Festival, Kat finds Maya passed out, seemingly dead! ...until she comes to, revealing she was simply in a candy coma from eating all of Kat's candy.
- Big Sister Instinct: Kat is very protective of Maya. It's partly deconstructed when not only does it border on overprotective, but she associates Maya's breathing attack with Carlos and the ghosts and wrongfully alienates both.
- Bittersweet Ending: On the bitter side, Maya's Cystic Fibrosis will eventually grow worse, and it's left ambiguous if her breathing tube is permanent or not. On the sweet side, however, Kat has overcome her fear of ghosts and Maya befriends one. Kat and Carlos are on much better terms now. Also, while they didn't get to meet their Abuela's ghost, the girls are surprised to find a mysterious feast of traditional Mexican food waiting for them in the dining room.
- Character Development: Kat goes from being anxious and afraid of ghosts to coming to terms with them.
- Hidden Depths: Although she's a very cheery and optimistic child, Maya does have a grasp on her mortality that borders on sobering.
- Ill Girl: Maya.
- Mood Whiplash: One minute, Maya is having the time of her life surrounded by the friendly ghosts. But then she drops her soda, and the breaking glass causes a panic among the ghosts that leads to her breathing attack.
- No Antagonist
- The Pollyanna: Maya has quite an abundance of energy and optimism about her.
- Reality Ensues: The book does not shy away from the fact that Cystic Fibrosis has no cure, and Maya's lungs will grow worse as she grows older.
- Rule of Symbolism: Raina Telgemeier points out that part of the book's theme is about breathing. Although Kat can breath normally when compared to Maya or the Ghosts, her anxiety makes it hard for her to embrace life as is.
- Shown Their Work: There's commentary showing all the research that went into creating this story.
- What the Hell, Hero?: Maya calls out Kat on letting her fears get the better of her.
- Yank the Dog's Chain: Maya's breathing attack while with the ghosts does not give Kat a good first impression of ghosts and even exacerbates her fear of them.
- "You!" Exclamation: Kat has this reaction to Carlos the second time she sees him.