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1. Uses a wand
Percy prefers the more classic option of sword
2. Controls water
Son of Poseidon or something...
3. Third wheel to his best friends' relationship
C'mon, let Ron and Hermione do their thing
4. Plays Quidditch
Considering Percy can't fly, I don't know how he would do this
5. Can talk to horses
Yes.
6. Has ADHD
Although, Harry does act like it sometimes
7. Was created first
The first HP book was released in 1997. The first PJ book came in 2005
8. Is an orphan
Thankfully Percy's parents aren't dead from an evil wizard
9. Has a scar
Somehow Jackson hasn't gotten one yet. Huh.
10. Has black hair
If I have to explain why PJ in the Disney+ show being blonde doesn't count, I swear—
11. Is the main character for 6 books
The HP series is 7 books. PJ is a lot longer.
12. More prominently uses a pen
His signature weapon, Riptide? The pen-sword?
13. Wears glasses
Percy has 20/20 vision, but he sure doesn't act like it
14. Is 13 at the start of his series
Harry is introduced as 11 years old. Percy is introduced at 12.
15. Attends a summer camp
Camp Half-Blood is a summer camp. Hogwarts is a regular magic school.