Several rocks are required to be exploded by bomb flowers in the cavern. It is possible to save a second here and there by rolling right before the rock explodes, which continues your momentum during the cutscene.
It is possible to skip the room with the water jugs and obtain the second small key early by using the fact that we can bring sticks through doors. First, unlock the door in the first room of DRC with the first small key to get rid of the lock. Go back to the first room, obtain a deku stick from the bokoblin and prepare yourself to bring the stick with you to the next room. To do that, throw the stick in a precise angle towards the door frame and open the door. The way the stick bounces on the door frame is RNG, but with good RNG the stick will go OoB through the door. If that happens, open the door and you will be able to use the stick in the main room. Then throw the stick behind the rock and attempt to roll over the rock, which is possible with a good roll and a good angle. Then attempt to bring the stick to the next room with you again. Then lit the stick with the fire torch and burn the wooden gate to obtain the 2nd small key early. This optimally saves 15s over getting it normally.
Note: Because throwing the stick OoB in the door frames is inconsistent due to being RNG, this is usually not attempted in runs.
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.
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.
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.
It is possible to reach the boss key area without the rising platform by jumping and landing on one of the fangs, and then jumping towards the hole in the wall. This is slower than sickass skip.
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.