Run 'n Gun

The levels in Cuphead are called "Run 'n Gun" levels. These levels are different from all the bosses in the game. You can actually collect coins in them and spend them(on this List of Shots or on this List of Charms) in Porkrind's Emporium. The Run 'n Gun levels are long levels with a lot of enemies. If you do not kill any enemies during a Run 'n Gun, you are granted the P rank, which is exclusive to Run 'n Guns.

Getting a P rank on every Run 'n Gun gives you the Black & White filter. You can find Forest Follies and Treetop Trouble in Inkwell Isle One, Funfair Fever and Funhouse Frazzle in Inkwell Isle Two and Perilous Piers and Rugged Ridge in Inkwell Isle Three.

There are no Run 'n Guns in Inkwell Hell or Inkwell Isle Four.

Completing all the Run 'n Gun levels with P rank will unlock the Black and White filter