The Deku Leaf is by far the hardest item to skip and is considered TAS-only to perform. Skipping the Deku Leaf first involves reaching Ganon's Tower early with Barrier Skip. Once in Ganon's Tower starts the real challenge.
By skipping the Deku Leaf, the normal Magic Meter is also skipped. This means that skipping the Deku Leaf also makes the Light Arrows unusable. While it is possible (theoretically) to obtain the Magic Meter from the Two Eye Reef Big Octo instead, that requires having Farore's Pearl which is also extremely difficult to obtain without the Deku Leaf and is also a much slower route.
Skipping the Deku Leaf saves several minutes in a TAS by skipping having to go to Forest Haven completely.
First, it is possible to skip the Trials by using a series of tricky item slides. Item slide to a door frame and then item slide to the horn above the Trial Door to grab it. You can then jump and grab a ledge to get on top of the very large door frame. On that door frame, there is a slope on the right side that you can clip through by item sliding sideways into it. This will make you fall down inside the door frame. You still don't quite have access to the loading zone from there, but there is a tiny gap in between the door and the wall, which you can item slide through to hit the loading zone.
After obtaining the light arrows, you will go back to the main room, where Phantom Ganon's final battle occurs. By performing a parry off a ground spawn from Phantom Ganon, with the right position and angle, you can land on the door frame without needing a zombie hover. From there, you can perform a very precise item slide in order to grab the wall without using the Deku Leaf:
NOTES on the item slide:
Once you've grabbed the wall, tap right (or left) and, as Link starts moving, hold all the way up on the control stick. Because Link can't climb up from that ledge, he will start sliding in the direction you chose. This slide will allow him to climb up the wall and go OoB on either the right or left side of the wall. It is very easy to get crushed once OoB: if you climb on the right side then jumping into the loading zone causes no issue, but if you climb on the left side you must make sure you pulled out your sword before the item slide, so that you can slash your way to the loading zone (one frame window).
This trick does NOT skip the light arrows, since Phantom Ganon will only spawn in that room if you did get them in the maze. This trick is required to skip Magic since you cant shoot light arrows without the Magic Meter.
Since you do not have Magic, skipping Puppet Ganon is also required if you want to skip the Deku Leaf. Start a Zombie Hover and, once on top of the room, wait for the Keeses to appear. Either snipe a keese with the bow (if you have the quiver) or pull out a bomb and get hit by a keese to drop it (if you have bombs). Kill a keese and collect his heart to skip Puppet Ganon.