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The Warp Zone is a hidden area that acts as a kind of teleportation system, connecting many worlds to one place. For the most part, they are sectioned-off areas containing Warp Pipes, although Super Mario Bros. 3 featured an entire island as its Warp Zone. Instead of Warp Zones, New Super Mario Bros. and two of its sequels feature Warp Cannons accessed from secret exists in certain levels, each of which would launch Mario or Luigi to a later world.
Using certain Vases within Subspace in Super Mario Bros. 2 automatically warps players to later worlds, without the use of an intermediary Warp Zone. In some episdoes of The Super Mario Bros. Super Show!, King Koopa would similarly use potions to create portals or doors to make his escape.
In Super Mario World, players can skip directly to the Front Door of Bowser's Castle by accessing the Star World via Star Roads connected to Donut Secret House, Vanilla Secret 1, Soda Lake or Forest Fortress, and then clearing the paths to the final warp (itself directly accessed from Valley of Bowser 4).
Similarly, New Super Mario Bros. U and New Super Luigi U have secret exits in some levels that allow users to skip to later worlds, as do New Super Mario Bros. and New Super Mario Bros. Wii. These special levels are the following (the first link of a pair indicates NSMBU level, the second link the NSLU level): Blooper's Secret Lair/Cheep Chomp Chase (in Acorn Plains) and Piranha Plants on Ice/Slippery Rope Ladders (in Layer-Cake Desert) leads to Soda Jungle, Skyward Stalk/Beanstalk Jungle (in Sparkling Waters) and Fliprus Lake/Fliprus Floes (in Frosted Glacier) leads to Rock-Candy Mines, Flight of the Para-Beetles/Para-Beetle Parade (in Soda Jungle) leads to Meringue Clouds.
Super Mario series
Super Mario Bros.
In Super Mario Bros., the zone is a sectioned-off area containing pipes to different levels. There are three, one located in World 1-2 and two in World 4-2. The first gives the choice to warp to World 2, World 3, or World 4, and is located behind the pipe that leads to the Flagpole. In World 4-2, the zone behind the final pipe leads to World 5 only. Instead, the player must find a secret Beanstalk in order to warp to World 6, World 7, or World 8. The first Warp Zone also lets players perform the famous Minus World glitch.
Super Mario Bros. The Lost Levels
In Super Mario Bros.: The Lost Levels, Warp Zones function identically to those in Super Mario Bros. They no longer, however, give the player a choice of destination, as every zone contains only one pipe. Some Warp Zones send the player to an earlier World; for instance, the Warp Zone in World 3-1 leads to World 1, and the Warp Zone in World 8-1 leads to World 5. However, the backwards Warp Zone in World 3-1 has a gap (so Mario can die before the time limit expires, instead of entering the pipe). This time, to prevent glitching by jumping over the flagpole, some Warp Zones are located over there.
Super Mario Bros. 3
In Super Mario Bros. 3, the Warp Zone consists of an island named World 9, that can only be accessed via Warp Whistle. Like other games' Warp Zones, it connects to the other kingdoms of the Mushroom World, although the zone itself is not completely interconnected; to access the top row, one must warp from World 1; to access the middle row, one must warp from Worlds 2-6; and to access the last row, one must warp from Worlds 7-9. Super Mario Advance 4: Super Mario Bros. 3 shortened the text at the top of the Warp Zone from "Welcome to Warp Zone" to "World 9 Warp Zone!". Although the world cannot actually be visited on the world map due to it requiring special circumstances to access, it was most likely the small island located to the east of Desert Land, the north of Giant Land, the south of Pipe Land, and the west of Dark Land, due to it being a small island of roughly the same shape as Warp Land, and it having the same colorization as Warp Zone.
Super Mario 3D Land / Super Mario 3D World
Warp Zones also appear in Super Mario 3D Land and Super Mario 3D World. They are in the same places as they were in the original Super Mario Bros., in World 1-2 and World 4-2. However, there is only one orange pipe, and they only warp the player to the next world.
Captain N: The Game Master
Characters in Captain N: The Game Master frequently used Warp Zones for means of rapid transit, with the Warp Zones of Super Mario Bros. even being referenced to in the show's first episode.
Super Paper Mario
A model of a Super Mario Bros.-style Warp Zone could be found in the underground section of Chapter 3-1 (itself a recreation of Super Mario Bros.'s World 1-2) in Super Paper Mario, though this Warp Zone took the player to other parts of the current level rather than different worlds. It did not serve any real function other than to take the player back to the overworld. The Warp Zone is also mentioned by a defeated Warping Pipe in Super Paper Mario, who believes it to be a fabled place where great warriors (apparently people with incredible skill over Warp Pipes) tread.