Flipper
One-Way Flippers are Doors that, once through, one cannot get back to the area before. This can prove to very annoying if the player exits through the doors and realize they forgot to get something important, such as a check point or a power-up. It forces the player to search everything that the area can offer rather than just running through the level as fast as possible.
They are commonly referred to as "Pinball flippers" because their shape resembles two flippers from a pinball game; just like in pinball, once an object passes through, it cannot and will not come back.
Originally debuting in Super Mario World 2: Yoshi's Island, the flippers showed up again in Super Mario Advance 4: Super Mario Bros. 3 during the stages Slidin' the Slopes, Doors o' Plenty, and Swinging Bars of Doom.
