P Warp Door

P Doors are Warp Doors that can only be entered when a P Switch is active. These Warp Doors made their first appearance in Super Mario Bros. 3, but with a different appearance from its current one.

Super Mario Bros. 3
A P Door first appears in Super Mario Bros. 3 in the second fortress of Giant Land. This P Door is invisible, and an outline of Silver Coins will show where to enter when the P Switch is pressed. P Doors also appeared in later fortresses including World 7-Fortress 1 and World 8-Fortress, this time in visible form, represented as a white rectangular doorway.

Super Mario World
In Super Mario World, P Doors appeared in the levels Donut Secret House, Vanilla Ghost House and Forest Ghost House. They had the same sprite as a Warp Door, but with a light blue palette.

Super Mario Maker
In Super Mario Maker, P Doors were introduced in the version 1.30 update. They were given new sprites for all styles, in the same blue as the P Switches with a white or blue "P". Unlike in Super Mario World, they are visible as outlines when not active.