The crossing the wall in Mario Bros is not something a "hack", "a lie", "a cheat", etc. ...
This is a "nature of the game," based on pixels.
How it works
The Mario sprite is a picture of 16x32 pixels (when large (after eating the mushroom), when small is 16x16 (before eating the mushrooms, or when you remove the power)), and the cinderblock wall the game are 16x16. The sprite of Mario crouch is 16x16 pixels, equal to the block wall.
When Mario goes with enough momentum, and is bent and measuring 16x16, and hits the top of the Mario sprite against a block of more than 8 pixels away from a block that is to the right, Mario will be right where the sprite is divided 16x16 pixel block with a right below. So, Mario will be as if on the ground and measuring 16x32 will be normal and spending and an auto scroll to the right, as Mario, cannot be inside a wall.
How to do?
It is basic and necessary to go as Super Mario (because it measures 16x32 pixels) or any other suite of Mario (except for Frog Mario, because not help much), but as Mario (16x16 pixels), it can, but is twice complicated.
The momentum (or level of "P") must be the medium to total (from two arrows on, until all coming to the "P" in the lower level of the screen).
When it has enough momentum (or the already mentioned), you must bow to Mario, and make the top of the Mario sprite (jumping course, but still crouched) tap a block that is superior to 8 pixel block wall.
If everything was done properly, let alone go to Mario, and he will move alone (to right).
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* You may talk of pixels in a game where you move sounds a bit complicated. Therefore you can choose to simplify. How? You can just try watching the video, and try to "imitate" until you get it. This will be as practical intelligence.
* Please note that these are "mistakes" or "bugs" in a game, not "hacks" or other changes in the game. And not are Game Genie codes.
* Also, most times, these tricks are used in videos TAS (Tool Assisted Speedrun) or TASes as a method of shorthand, and save time.
* Not if you see this trick in a video (I speak for me), not exactly a TAS. But nevertheless, these tricks are done in TAS, as it has a greater ease in doing so.
I hope this is helpful.
If you have questions, you can write it, in comments.
Regards.
::Vlass::
EDIT 08-15-10: 29,000 plays.. Thank you!..