After unlock Boss Rush mode
hold I then enter Boss Rush, the bosses will change to their Ultimate Mode self
Hold N then enter Boss Rush, Zangetsu will have all special abilities including charge slash
Hold T then enter Boss Rush, player will have infinity ammo for sub weapons
Hold C then enter Boss Rush, the already-eaten sub weapons and recovery items will be restored after next boss
(PC version, I think secret commands of console versions are already figured out by others
I wanna retreat the wild words I posted but I still feel the Boss Rush mode unpolished; having no HP extend really sucks
The key disappointment: can't fight the standalone Demon Zangetsu boss battle, waiting for update lol)
https://twitter.com/Aceearly1993/status/1001006320768532480