It turns out the
Bloodstained: Ritual of the Night Classic Mode has a secret 1986 Mode variant. If people enter a secret code, which is the infamous Konami code, after selecting Classic Mode, it unlocks. They then can see if they can survive the five levels with new limitations on them. [Thanks, IGN!]
Accessing the new mode isn’t difficult. Choose Extra Mode from the game’s main menu. Then, choose Classic Mode. On that screen, press up, up, down, down, left, right, left, then right. Then, if you’re on the Switch, press Y, then A. If you’re using an Xbox One controller, press X, then B. PS4 users would press square, then circle. 1986 Mode will appear at the bottom of the screen, below “Return to Menu.”