Shelf Shift
Shelft Shift is a trick involving the door in the Throne Room that moves Link between Hyrule Castle and the Sewers. The game considers these two as separate dungeons, and walking through this door updates a value in the game's memory to change the dungeon from Hyrule Castle to the Sewers. This is a unique property, as no other door in the underworld is capable of moving Link between dungeons.
With the use of other Major Glitches, players can access this door from dungeons other than the intended Hyrule Castle and Sewer pairing. The routine the Throne Room door uses to update the dungeon ID value is still used, meaning all dungeons in the game are paired, and walking through this door with any dungeon loaded will change the dungeon ID value to its corresponding pair. This trick is useful for manipulating which dungeons the game thinks you're in, and it can therefore be used to bypass certain overworld entry requirements.
Another thing to note is that you will need some way to get rid of the shelf in order to perform this trick. You must either have Zelda as a follower and the lamp in your inventory or you must despawn the sprites by desyncing Link's coordinate and Room IDs (usually done by wrapping the underworld map).
Pairs
- Hyrule Castle and Sewers
- Eastern and Desert Palace
- Agahnim's Tower and Swamp Palace
- Palace of Darkness and Misery Mire
- Skull Woods and Ice Palace
- Tower of Hera and Thieves' Town
- Turtle Rock and Ganon's Tower
So for example, if a player enters Agahnim's Tower from the overworld, then EGs to Throne Room and uses the door, the game will consider the player to be in Swamp Palace.
Application in Swordless Speedruns
In the Swordless speedrun, Misery Mire must be completed without using the Ether Medallion, as using any of the Medallions requires Link to have a sword. This presents a problem as there is no known way to enter Misery Mire from the Overworld without using Ether to unlock it. The solution is to use a Shelf Shift starting from Palace of Darkness. This will allow the player to obtain the Misery Mire crystal without ever having to use (or even collect) the Ether Medallion.
