Boss Rush

Boss Rush is a game mode unlocked by unlocking the Forge shortcut. It is accessed from the elevator room, and costs 3 to use (except for the first time, which is free). Completing Boss Rush unlocks Bracket Key.

In Boss Rush, each floor only contains an entrance, boss rooms, and an exit. Bosses do not have a damage per second cap in Boss Rush. Boss rewards are the same as the main game, including Master Rounds should a boss be killed without taking damage, though refraining from picking up a gun on the floor will not guarantee gun drops from later bosses on the floor. Defeated bosses will not drop during this mode.

Bugs

 * Using the elevator to traverse to a Non-boss rush floor will result in you being required to pay 3 credits, regardless of whether or not you’ve used Boss Rush before. If you pay the 3 required to enter Boss Rush and then leave the game, you will need to pay it again.
 * This bug also occurs if you exit the game after Tinker has just finished constructing the elevator and offers you a free first go.