This switch can be hit with the slingshot, boomerang, bomb, and bombchu. It can also be hit with the sword or a deku stick with a difficult hover off the nuts of the Octoroks.
This is the biggest sequence break for this dungeon. With it you can skip everything between getting the Boomerang and the last room before the boss. It skips killing the tentacles, Big Octo, and a few other rooms. There are two parts: getting over the gap in the room with the raising platform and getting through the door.
Skipping Bigocto requires you to get over a large gap in the raising platform room. There are multiple methods for crossing it, but these are the most useful.
A well angled megaflip from the left ledge will make it
Recently, there has been increasing use of a megaflip using one of the boxes in the elevator room. It can be seen here.
A more difficult megaflip from a Biri can also make it over the gap. The area where you can start the megaflip from and still make it is small, and requires you to be as close to the ledge as possible. By luring the Biri, you can give yourself enough time to set up for a megaflip from it. Having ISG greatly helps position yourself near the ledge.
Using the Biri, you can hover up to the ledge after the miniboss, and then lower the platform like normal.
The first method found. You need a bottle with a bug or fish to do this trick. Using ocarina items allows you to keep the item in the bottle.
Ocarina items method:
Bottle switch trick:
This was the second method found, and significantly harder than the bottle switch trick. However, it can be done without a bottle, so it was used commonly until Method 3 was discovered.
This was the latest method found, and the fastest, and best of all, it only requires a sword.
Line up against the wall beneath the switch and pull out a bombchu. Release it on the 5th flash and it should activate the switch.
Pull out the boomerang and aim as high as possible, and just a little left of the web. As soon as you release it, start sidehopping and when it starts coming back it should hit the switch.
You can also use jelly hovering to reach Big Octo's room without killing the tentacles. He can be defeated with just a weapon, but a deku nut makes him much easier.
It is possible to megasidehop into the loading zone as an adult. This used to be extremely difficult, but new setups have been found that make it much easier.
1) Get ISG and get in the corner I do in the video. Try not to take forever like I do.
2) Do the backflip/sidehop/siderolls I do to get in position, then walk directly forward. You will lock onto the edge due to ISG.
3) Pull out a chu and pause buffer to the first fast flash (9th flash). Sidehop shield to the right and hold shield. (Z+R+A+right). It is possible to use a bomb as well but the cue isn't as clear (2nd red frame of 2nd fast flash iirc).
4) Aim the joystick to the upper right so Link is walking facing diagonally. The aiming should be near the edge where Link will be sidewalking. There is a very small range RIGHT at this edge where the chu behaves differently for some reason, but there is about a 10degree range where the chu will work correctly.
5) Pull out a chu and pause buffer until the black frame immediately after the 8th flash (when it starts flashing quickly). At this frame, press and hold R, and hold right (holding right is for a cue on step 6). Note: You can aim while waiting for the chu as I do in the video.
6) After dropping the chu, pause buffer advance four frames. At this frame, Link has just started shifting right. One visual for this is you can barely see a bit of shield on the left side of Link, but just look at the video. On this frame, release the analog stick and press A to roll.
7) Advance a fair number of frame to the end of the roll. You want the second explosion frame, which is when the explosion is just of moderate size (see video). On this frame, hold shield if you aren't already, and sidehop left (R+A+left). Hold until you clip.
8) If you did everything right, you should be in Jabu Jabu.