Solution: META: Percy Jackson
Answer: DINOSAURSBEFOREDARK

Written by Ethan

Trying to directly put your answers into the blanks doesn't work. However, noticing the theme of Percy Jackson and Greek myths, one may realize that each of the answers clues a Greek mythological monster. All of the referenced monsters are met in one of the Percy Jackson books, though this information is not needed to solve the puzzle. Taking the letters in the numbered given at the bottom gives FIRST MAGIC TREE HOUSE, cluing the first Magic Tree House book, DINOSAURS BEFORE DARK.

BookAnswerMonsterReasoning
Harry PotterRIDDLESPHINXThe Sphinx tells riddles and devours those who cannot answer
The Maze RunnerLABYRINTHMINOTAURThe Minotaur is trapped in the Labyrinth.
Lord of the RingsEAGLEHEADGRIFFINGriffins have the head of an eagle.
I Am Number FourTHREECERBERUSCerberus is a three-headed dog
Treasure IslandWHIRLPOOLCHARYBDISCharybdis creates giant whirlpools which sink ships.
Miss Peregrine's HomeBIRDSOFMETALSTYMPHALIAN BIRDSThe Stymphalian Birds are birds with metal beaks and feathers.
Six of CrowsFIREBREATHERCHIMERAChimeras are firebreathing monsters.
The Hunger GamesSTONERMEDUSAMedusa turns people to stone.
DivergentREGENERATIONHYDRAThe Hydra has the power of regenerating heads.

Author’s Notes

This puzzle went through 3 complete rewrites. The first two times had extremely boring mechanics that aren't worth mentioning. I wrote those versions before I had looked at other hunts' metas, which was definitely a mistake. When I came up with this mechanic, I ended up having to redo 7 of the original 9 puzzles, which was unfortunate, but definitely necessary. I've definitely learned to have a solid meta idea before writing all of the feeder puzzles. Though this meta is not super difficult, it's at least more interesting than before.