Has to be 10 DIFFERENT bosses! Cannot be the same boss!
I went across Isles 1, 2 and 3 and beat 10 different bosses on simple difficulty!
Any boss counts
The bosses i recommend are:
1. Root Pack
2. Goopy Le Grande
3. Captain Brineybeard
4. Werner Werman
5. The Moonshine Mob
6. Cagney Carnation
7. Ribby & Croaks
8. Sally Stageplay
9. Hilda Berg
10. Baroness Von Bon Bon