When a seemingly-pointless character, object or place turns out to be a necessary plot point
- Doubledork: "Harry, there's one thing you need to know about these stories. If something is mentioned 20 times during the book, it's not important. But if it's mentioned just once, the whole story depends on it! Which reminds me, I'd like you to meet my pet phoenix, Squawkes. He has amazing powers!"Harry: "Amazing? Like what?"Doubledork: "Like, anything J.K. Rowling needs to throw in just to get through the plot! That's the amazing part!"-- "Harry Plodder and the Lamest of Sequels", MAD #424
- The cartoon cat from Last Action Hero.
- The Harry Potter franchise has many examples of this trope:
- Professor Quirrel in Harry Potterandthe Philosopher'sStone. At first, he's just a stuttering Defense Against the Dark Arts teacher. It turns out by the end he's the one carrying Voldermort's face on the back of his head.
- Fawkes from Harry Potterandthe Chamberof Secrets. Dumbledore's pet phoenix doesn't seem to be important, but in the end, it brings Tom Riddle's diary and the sword of Gryffindor, blinds the basilik, and heals Harry's wound.
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