A skew bounce is a glitch that can be used to reach places Link can't normally get to by simply jumping. It's most useful inside of shrines, due to shrine walls being unclimbable, but can also be useful as a method of entering bullet time without needing to jump off of anything when in combat. There are two methods for setting the skew needed for a bounce:
The easiest method is slightly slower due to Link going into the ragdoll state. First, stand Link at the top of a slope. Shield jump down the slope by holding forward on the left analog stick, pressing X, and then pressing ZL and A at the same time. Next, you want to pull out the bow (ZR) to enter bullet time. Once in bullet time, use the left analog stick to turn Link around as close to 180° as you can get, and land on the slope facing backward.
The more difficult method is slightly faster than the easy method due to Link not going into the ragdoll state. First, stand Link at the top of a slope. Hold down ZL to shield (continue holding until noted), then turn the camera around close to 180° so that Link is facing toward the camera. Next, you want to hold down on the left analog stick, jump down the slope (X), tap R to turn Link around midair, press A to shield jump (ZL should still be held, and can be released after pressing A), and then finally press ZR to pull out the bow and enter bullet time. Link should land on his shield in bullet time and facing backward.
The bounce skew should now be stored (until cleared), and can be used when needed. Shield surfing or closing the game software will clear the skew state, just as with any other type of skew. In order to use the bounce, shield jump in place (X, then ZL+A) and unequip your shield before hitting the ground (using the d-pad-left quick menu). Skew bounces can work while moving, but the results are inconsistent and unpredictable, so it's best to use them while standing in place.
You may notice that during a skew bounce, Link will have a horizontal movement along with the upward bounce. The direction of Link's horizontal movement is determined by the direction of the slope the skew was set on. For example, if the top of the slope is to the south and the bottom of the slope is to the north, Link's horizontal movement will be northward. Using the horizontal movement in combination with the upward bounce can be advantageous in many situations, so it's advised to set your skew for the bounce in the general direction you want to move in.
After doing a skew bounce, Link will be left with an unusual type of skew that can cause him to immediately ragdoll upon shield surfing, making it time consuming and frustrating to clear the skew state. This happens when Link shield jumps on flat ground in a direction parallel to the direction of his skew.
On flat ground, it's best to clear your skew with a shield jump in a direction perpendicular to the direction of Link's skew. This will result in Link skewing very strongly to one side and then landing on his shield as intended. If Link's shield doesn't slide on the surface, it's best to do a second shield jump or shield surf in order to fully clear skew.
Shield surfing down a slope (even in a direction parallel to the skew) usually results in Link having enough room to miss the ground, and he will land right-side up on his shield. This can depend on the strength of the skew and the steepness of the slope, but for the most part is consistent. This is generally the most ideal method of clearing a bounce skew in a speedrun, as it takes up the least amount of time, but can be dependent on location.
It's important to note that skew bounces will leave Link with ragdoll glitch, so make sure to clear that as needed.