See Kokiri Forest: Enter the Deku Tree as an Adult for more information.
After entering Deku Tree, it is possible to get reach Basement 1 right away by using the ladder on the ground floor of the Tree. Position yourself at a slight angle from the ladder and hookshot the side further from Link near the top. When done correctly, Link should grab the edge of the platform instead of the ladder. Once hanging from the edge, simply press A to let go and then press B to jumpslash. Once you land in the unloaded Basement 1, you can climb up the vines about halfway until you reach the loading area for Basement 1 and then drop down again.
After doing the above trick, you will still have to get to the second basement. Jump on the chest by the torch and pull out the bow. Shoot an arrow through the torch at the web to order to gain access to the second basement.
It is possible with a very precise angle to clip through the first room in the Deku Tree as an adult using a superslide with the hover boots on to slide out of bounds, then at the right moment take them off and sidehop then jumpslash to recoil off the wall. If done correctly you will hit the loading zone right into Gohma's Room. Video: Twitch highlight from Sockfolder
Bring out your Deku Stick just as you are about to climb the vine to prevent the first Navi text.
Either backflip onto the chest then jump to the wall or take out your sword or a deku stick when you come near the vine to delay the text then quickly grab on before it activates.
When climbing the vine you can use the highest skulltula to damage boost you up to the walkway. The timing for the skulltula is random. A small trick which can aid you in performing this trick, is that you can climb a rung, stop, climb a rung, stop. Which will make the skulltula, even if it sees you, activate and then deactivate. That way you can get the rung or two higher you need before climbing up a bunch and having it finally hit you. That said, the fastest way is to simply get lucky however and get the boost without stopping at all.
Just before you enter this room, you can avoid activating the door text. Get about a sidehop distance away from the door, then sidehop in front of it and press A as you are coming down to open the door. Once inside, instead of waiting for the Deku Scrub to attack, go around it and head towards the other end of the room. Deflect the Deku Nut back at it, then roll into the center to immediately catch the Deku Scrub.
When you shoot the ladder in the slingshot room you can move during the cutscene. Use this time to walk to where the ladder drops so that you can climb it as soon as possible.
From where you climb the vines to the top of the room, face the vines. Jump off and then fall a short distance, then jumpslash. You should ricochet off the wall and then fall down and break the web. Immediately jumpslash a second time and you should then ricochet off the wall and onto or near the switch (depending on your accuracy).
Break the first web by climbing to the top of the Deku Tree, but before you fall down to the basement, either quickly run to the vines or backflip off the web as it breaks. Now set yourself up at the very edge of the hole as shown in the video and align using the deku baba or C up - the angle isn't overly precise. From here, sidehop to the left and then jumpslash against the wall at the same time as you see the black wall markings come on to the screen. The timing of the jumpslash is fairly precise. Effectively, one is trying to recoil off the very bottom of the hole, which in turn causes an anti-gravity glitch, which sticks Link against the ceiling for a moment and thus gives him just enough extra distance from the recoil to land next to the web in the basement.
This can also be done by directly after breaking the web with a different setup.
If you jump off the top to break the web, you can backflip or sidehop as soon as you hit the web to avoid falling to the below floor. This is useful if you are setting up the Deku Baba Mega Sidehop.
Using the Deku Baba closest to the vines leading to the basement, attempt a megaflip off of it but instead of a backflip (which will give you too much momentum) use a sidehop. When angled right, this will bring you over to the web side of the lower basement, essentially skipping the lower half of the dungeon.
Break the first web by jumping on it from a great height. The aim is to keep B1 unloaded as you break the web. This can be done by either using the Web Backflip mentioned above or, more commonly, running onto the vines as the web is breaking, thus preventing you from falling down to B1 and loading the second web. With the first web broken, perform the Deku Mega Sidehop or the B1 Jumpslash and as soon as you land on the platform below backwalk to the ledge and you can clip through the web. Alternatively, one can backflip twice immediately upon landing to fall through the unloaded web.
If, upon breaking the first web, you are not able to reach the vines and instead fall down to the basement below, hold Z as soon as this is apparent. This will keep the camera directly behind Link and away from the web in B1, and as a result the web will not load, allowing you to climb back up and still ultimately clip through the second web.
This is an alternative to the Baba Mega Sidehop. Activate ISG, preferably off of the chest with a recovery heart in it. Now stand at the edge of the ledge and face the Gold Skulltula but a little to the left. Now turn sideways and sidehop into it and you should hover on it. Hover right and left about 7-10 times then you should be able to backflip to the above ledge. You can also make it quicker by megaflipping. About 1.5 seconds after it last hits your shield, roll then backflip when you come up and it should megaflip. Note that the key thing in timing this is that the Gold Skulltula can only hit your shield in a set interval, so you can time the hits to know when to sidehop, or when to megaflip.
This is a faster way to do the above hover. Once you are in the air for the first hover, just wait about 1 second, then roll and backflip when you come up for a megaflip which should get you to the ledge.
Get exactly 15 rungs above the Gold Skulltula on the basement vines then press A to fall and hold up, then you will grab the vines right above the skulltula and the skulltula will clip you through the vines. If it was angled right you will fall into OoB water. You can now swim around the room and can fall to the deku scrub room without having to burn the web.
One way to reach the second basement as an Adult if you don't have the bow is to superslide warp. You cannot preform this trick if you have any strength upgrades. Go over to the grassy shrubs by the deku baba and position yourself at a slight angle so you won't get stuck against the wall. Back just out of the shrub's "Grab" range and make sure that the baba doesn't immediately try to hit you. Just as the baba gets ready to strike, roll and press A to try to grab the shrub. If done correctly, the baba should hit your shield, causing you to preform a superslide. Once you slide as far as you can into the water, let go of R to superslide warp out of bounds. From here, swim to basement 2.
Another way to reach the second basement as an adult without the bow is to clip through a wall using the hookshot. Go to the torch which is closest to the Skulltula on the west side of the room. Get ISG and do a very precise backflip onto the ledge with the torch. If done right, you can then clip through the torch by mashing the hookshot button while z targeting.
The second video shows an easier setup for this.
Get on the submerged platform in the water near the right side of the basement 2 ledge. Roll off of it and hold forward on the control stick to grab the ledge. Since you can't do web clip after doing this trick, you'll need to use flame storage to burn the web.
By learning the boundaries of the text message trigger, you can stay on the very edge of it, and if timed VERY well, you can (if you were in the correct position) backflip over it. You should clip your toes on the very edge of the ledge and then fall off. This gives link a tiny bit of extra height which is necessary in order to land on the platform which should have just arrived in it's closest position to the edge.
This trick utilizes the Jumpslash Method of Flame Storage in order to skip pushing the block. Climb up onto the block that you would normally push off the ledge. Face the torch on the wall then jump off of the block and jumpslash the torch. If you hit it high enough and in the correct spot, when you take out a deku stick it will burst into flames. Now go burn the web. This trick can be done with 100% accuracy with practice.edit
Using the infinite sword glitch and with a correctly timed and positioned backflip, you can use Gohma to clip behind the wall covering the door, allowing you to exit the boss room after. This is the fastest-known method to reload the boss room after defeating Gohma to perform the Ganondoor Wrong Warp later on.