Boss Rush is a mode in the game Five Nights at Fuckboys 2. In it, you will fight every boss from the game ( The Puppets and BB included ) Also, you will be capped at level 1, and your attack power is set to 25%.
To unlock the Boss Rush mode, you need to have beaten every single camera in the game and listen to BB's speech. After that, when you enter the Parts/Services room, a giant crystal will appear asking if wish to play the mode. To play it you need to have a password which is revealed after beating the final boss.