Defeat every boss in the game including both of Dracula’s forms, and both of the optional Legion battles. Once this is done, you can go to any warp room and enter the boss rush mode by sitting in the chair.
Boss Order:
1. Crazy Armor Lv.9
2. Wyvern Lv.14
3. Trevor
4. Skeleton Diver Lv.24
5. Minotaurus Lv.30
6. Isaac Lv.34
7. Saint Germain Lv.37
8. Trevor Lv.40
9. Dullahan Lv.49
10. Isaac Lv.50
11. Death Lv. 51
12. Legion Lv.52
13. Nuclais Lv.53
14. Dracula
15. Dracula’s Ghost
The Reward for Boss Rush Mode is unlocking the Sound Mode
Boss Order:
1. Crazy Armor Lv.9
2. Wyvern Lv.14
3. Trevor
4. Skeleton Diver Lv.24
5. Minotaurus Lv.30
6. Isaac Lv.34
7. Saint Germain Lv.37
8. Trevor Lv.40
9. Dullahan Lv.49
10. Isaac Lv.50
11. Death Lv. 51
12. Legion Lv.52
13. Nuclais Lv.53
14. Dracula
15. Dracula’s Ghost
The Reward for Boss Rush Mode is unlocking the Sound Mode