Flipper
One-Way Flippers are Doors that, once passed through, prevents access to the area before. Players who find a set of these in a level should remember to make sure they have all the desired items/collectibles before passing through the flippers.
They are commonly referred to as "pinball flippers" due to their resemblance to flippers from a pinball game.
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.
The One-Way Flippers also appeared in level 2-3 of New Super Mario Bros. and were originally going to appear in New Super Mario Bros. Wii.
They also reappear in New Super Mario Bros. 2 in a few levels, including a Ghost House.
