Simply jump across on the first sidle, then sidehop and jumpslash on the second.
It is also possible to perform a frame perfect roll clip to skip the second gap. This is especially useful when Link is swordless.
Slash the four ropes on the second level bridge, then wait a few seconds. Go forward then the bridge will break. When you're close to the switch, press B to jumpslash and then jump off.
After entering the main hub room from the entrance room, perform an Item Slide charged up against the door. Then hold forward and press B to do a forward slash. Link will grab the ledge on the other side of the room, and from here you can use the grapple hook to unbar the door.
After performing one of the boss key shortcut method, you need to use the grappling hook to unbar the door. The cutscene of the door unlocking is actually composed of 2 cutscenes, and there is one frame to do an input in between them. By pressing A on that frame, it is possible to let go of the grapple target mid-cutscene. This saves time as it skips having to swing for a bit after taking control of Link back.
Pick up the pot on the right side of the boss door and place it on the nearby ledge near the wall. Drop down and perform a partial Ledge Clip with it to then climb up and perform a Roll Clip to the right. Then just fly with the Leaf into the loading zone.
Diminish your health to 1/4 heart. Attack the magtail so that it curls up into a ball and place it below the top ledge on the right side. Throw the small pot with a fairy in it forward and back up to grab the ledge with Link's sword out. When the magtail uncurls, it should damage Link and kill him. Zombie hover off of the damage, and once you are above the boss door, the fairy will hopefully heal you. Go to either the right of left side and stand on the horns jutting out of the side. Align yourself (more specific alignment to come) and roll or backflip. If done properly, you should clip through the ceiling without being crushed and either still be on top of the overhang, or have fallen but remained OoB. Either way, make your way towards the loading zone and jump in.