Sewer door deletion
You delete this door by copying the state of the big key door in the Tower of Hera over it. You have to have opened that door first, or else the door you copy will still be closed.
Deleting the sewer door is an effect that persists when you save your game.
You should hit a star tile, and not open the select menu, before performing this glitch. That will prevent heavy VRAM corruption from being one of its effects. The glitch still works if you don't take this precaution, but you'll have to save and quit and then hard reset, and also it might crash a Super NT.
To start, face the door and throw a somaria block into it. Move a bit into the door and pick up the block.
Once you're somewhat into the door, you can tap up to snap to a lower position, and you can throw the somaria block to the left to bounce off the door frame and get it deeper into the door.
When you're deep enough in the door, you'll snap into a position where you can hold up the block and only see the block, not Link, as shown above. From this position, don't throw the block left anymore -- you'll throw it over the wall.
You need to get still deeper to juke the door. Face up, throw the block, move exactly 2 pixels down while the block is in the air, and pick up the block again.
An effective way to move exactly 2 pixels is to boots-buffer twice (tapping down and A at the same time) while the block is in the air.
Tap up while holding the block. You should end up in a position 8 pixels lower, where you can see half of the block. You have now juked the door -- you're past the transition.
Now you need to get back above the door transition while the block is below it. Face up, throw the block, and boots-buffer up once.
Pick up the block again, and don't press a direction -- that would snap your position again, and undo what you did. You should be able to see about 3/4 of the block sticking out of the door now.
Throw the block (without pressing a direction), and wait for it to land. Then tap down. If you hit a star tile earlier, the screen will scroll down a little farther, and you might see some light visual corruption -- you can mirror and go on with your game.
If you didn't hit a star tile, you'll get heavy VRAM corruption, and then you should save and quit and hard-reset the game. Either way, you did the glitch, and the effect will be saved.
If you get not-quite-as-heavy VRAM corruption, where you can still see the select menu and the graphics are normal after saving and quitting, it may be that you forgot to open the big key door before copying it with this glitch, or pushed down from the wrong position. Or it may be that you hit select before the glitch, which you should avoid.
Bring two red bottles to the Tower of Hera so you can do two YBAs. You won't have an opportunity to take damage or use magic in between.
Make sure you're not at full health. Move until the door (by holding out your sword or boots-buffering) until you're on the bottom pixel you can be on. On the Link sprite, two rows of Link's hat are visible.
Equip a red potion, and press down and Y simultaneously. The screen will fade to an ellipse that's mostly off the bottom of the screen.
A side effect of a downward YBA is to Door Juke you past the door transition, so now you need to back up to line up for the second YBA.
Carefully tap left or right until you reach this position. You can't see Link, but you can tell by the way the camera moves. A row of lighter pixels on the doorway -- the second from the bottom of the screen, which is the third from the base of the door -- should be the bottom pixel on your screen. If you overshoot by one pixel, it's okay.
Do a YBA again -- select a red potion, and press down and Y simultaneously. The screen fades out again.
You won't be able to see the effect, but if you successfully did the two YBAs, the sewer door will be deleted. You can mirror out or save and quit, and go on to do the glitch you're deleting the throne door for, which is presumably dungeon ID swapping.
Unfortunately, you only get one chance at the second YBA.