Easy
11. Seaweed Brain
12. Two
13. 12
14. Above their head
15. War

Medium
11. Daedalus
12. Shadow Travel
13. The stars
14. Six
15. Elizabeth

Hard
11. Nine
12. Percy Jackson and the Stolen Chariot, Percy Jackson and the Bronze Dragon, Percy Jackson and the Sword of Hades
13. A parent's hand
14. Blue
15. Hecate