Boss Rush Cheat Codes
You can put modifiers on your boss rush runs if you hold down one of the following buttons and then press start on boss rush:
i – Nightmare Mode Boss Difficulty
N – Ultimate Zangetsu (normal boss difficulty)
T – Infinite Weapon Points
C – Subweapons and Hearts Regenerate After Each Battle
Multiple of these can be active at once, assuming you can manage holding down all the buttons and still press start.