SMB: Wrong Warp (4-2)

The traditional way to find Warp Zone in World 4-2 of the original Super Mario Bros is to climb a vine hidden in an overhead block. Located barely one screen to the right of the vine, happens to be a pipe that leads to an underground coin cache.

By virtue of the Warp Zone and the Coin Cache being so close together, it's possible to trick the game into sending you to the Warp Zone area instead of the Coin Cache.

Normally, Mario's on-screen position is beneath your coin count. By shifting him far enough to the right, closer to the "W" in "World", (with the screen still scrolled to the left), the game will still have the value for the Warp Zone area as your destination instead of the coin room. When Mario re-appears on-screen after going down the pipe, he's loaded into the Warp Zone without the vine.

 

There are a few different ways to shift Mario the required 20-30 pixels to the right for this trick to work.

The most popular method is with a "Backwards Bump".  Mario's on-screen position changes by several pixels anytime he brushes a wall while jumping backwards - He moves ahead slightly further than the screen scrolls.

Another technique involves jumping or sliding under the first set of blocks by crouching as Super Mario. Stand up while underneath the blocks, and the game will shift Mario through the wall and to the right of the screen.

As long as Mario is still shifted to the right when he enters the pipe, he'll go directly to the above-ground Warp Zone area.

 (The glitch even works in the Super Mario All-Stars version)

The ability to skip past the vine and onto Warp Zone saves precious seconds for speed runs. It's also really neat to learn what's happening behind the scenes... The first video features the evolution of all fastest known routes leading up to and including the discovery of "Wrong Warp". The other clips specifically discuss the World 4-2 Wrong Warp glitch:

4-2: The History of Super Mario Bros.' Most Infamous Level (20 min, 30 sec) by Summoning Salt
https://www.youtube.com/watch?v=i1AHCaokqhg

Darbian explains Wrong-Warp (3:23)
https://www.youtube.com/watch?v=7mIrKJ_s9qQ

SMB1 4-2 wrong warp tutorial/explanation (3:44) by andrewg1990
https://www.youtube.com/watch?v=U5B9rcL98ao