Recently a new glitch was found called Stale Reference Manipulation, or SRM for short. Its a glitch that allows for manipulating actor data, and one of the big main uses of it is being able to change what's in a chest.
There's a separate, much older glitch called Get Item Manipulation, or GIM. This works by delaying an item pickup animation, going in front of a chest, then going in water, and you will receive an item based on what item was on the chest (though it is not the item that was in the chest. For example, a recovery heart chest would give light arrows).
One chest item with very unique properties for GIM is Zelda's Letter. When doing GIM with a Zelda's Letter chest, you can get any item when you enter the water, and the item is based on the control stick angle relative to the camera. The problem is that normally no chest has Zelda's Letter in it.
But with SRM, you can change a chest to contain Zelda's Letter. Then set up GIM, and you can start getting all the items you need.
This is obviously a pretty massive glitch, and if it were used to its full potential in a No Source Requirement 100% run, where it doesn't matter how the items are gotten, it would probably save over an hour. However, I'm doing this run at GDQ soon, and using this glitch to just get every item wouldn't be the most exciting run to watch. So instead, I've made a route that makes use of the glitch to get some items that are not very interesting to get normally or skip a lot of cutscenes, and wont be using it for items that have other cool and unique tricks, so the route overall is pretty interesting. Because of this, the timesave for this route will likely only be a few minutes.
The items I'm getting with it in this route are: Dins Fire, Farore's Wind, Hammer, Ocarina of Time, Light Arrows, Iron Boots, Requiem of Spirit, Epona's Song, and 1 heart container.
This very likely also has applications for regular 100%, though its going to be much more complicated to figure out exactly how it will work out for that category and will likely take a while.