Those “books” are to supports to the level 12 pool of monsters.
Level 12 Support "Books"
https://duelistsunite.b-cdn.net/optimized/2X/a/a1f5bcabe819acad95fc7633ccc8827df7819fc9_2_701x1023.jpeg
art
3.0
1
psct
4.0
1
creativity
3.0
1
balance
3.0
1