A Link to the Past - Magic Mirror GlitchAlthough there is indeed a 'glitches' page for ALttP, I felt that this glitch is both very significant, but also not very well known. Therefore I decided to give this particular bug it's own page.
Note that this glitch works on BOTH versions of A Link to the Past; it can be performed on both the SNES and GBA adaptations of the game. It can be used to get into the Palace of the Four Sword in the GBA version, without the need of completing the Four Swords multiplayer adventure beforehand.
In order to 'activate' the glitch, you need to be inside a dungeon, and you need to equip the magic mirror. Next, find a ledge, and jump off it. Just as Link jumps off the ledge, use the magic mirror (because of the nature of the mirror, it is far more convenient if you attempt the glitch on a ledge that is right by a dungeon entrance, a feature notably present in the Thieves Den). If you performed the technique correctly, you should hear Link yell whilst the magic mirror warps him back to the start of the dungeon.
If you perform the technique incorrectly, you will either be warped and not hear Link yell, or Link will jump all the way down the ledge. The glitch can be tricky to pull off, as it's all about whether you get lucky enough in timing the use of the mirror correctly.
When you have performed the glitch correctly, place a bomb next to you, let it explode and hurt Link, and notice what happens. You can do this anywhere in the dungeon you want, as long as you do not perform any actions that 'deactivate' the glitch. You may walk around and bring up the pause/inventory screens without deactivating the glitch, but the following actions will deactivate: Using any item (except the bomb which you use to blow up Link), jumping off a ledge (using stairs is OK though), taking ANY kind of damage (so avoid hostile enemies/obstacles).
An example of the glitch being performed can be found below:
As mentioned earlier, you can also use the glitch in the GBA version of the game to get into the Palace of the Four Sword, which is shown in the video below.