At the Name Save File screen, enter "WSWWAEAW" or "X&BUTT". Butt Mode replaces many of the game's common nouns with the word "butt." Shovel Knight becomes "Butt Butt." "Fate" becomes "Butt." Shield Knight is "Shield Butt." And so on. Do note that Feats and Steam Achievements will be disabled while the code is active.