Down A is a glitch in the game that gives you the ability to walk through actors Link can interact with. You can also walk up seams you normally can't walk on, for example the slippery seams on the way to Goron Race.
Now you should be able to walk around and have "Down" shown in the A button. Jumping off a ledge, or grabbing a ledge of any kind will cause Link to revert back to normal. This can be worked around by backflipping or sidehopping off of ledges. Leaving an area will also revert Link back to normal.
When you perform Down A either being Swordless or having the B button dimmed (be inside a house) the buttons X,Y,1,2 will not be updated from their current state, meaning that if you had an usable item in one of these buttons, perform Down A and switch with an item you normally can't use, you're gonna be able to use it making this another method of Restricted Items
This method of Down A doesn't use Mask Storage, instead it uses the weird state of using the pictobox. Just like Restricted Items, you go into View mode, snap a picture and save it, after the game saves the picture there are these few extra frames of Link still being "in the picto state." One of the ways to exploit this is by taking a pic right as a source of damage (like a bomb for instance) is about to damage Link, hold R to shield as soon as possible to shield the damage. Link will be pushed back by the explosion hang off the ledge, but because of the picto state Link will continue to shield while grabbing the ledge and shield once more from the explosion resulting on walking around with Down A.
When you're in Down A mode, the camera is going to act weird and will always be above Link. Holding target will not place the camera behind Link but can mess up your movement while walking.
3DS users with the Circle Pad Pro or the C-Stick on the New 3DS can free the camera position while in Down A and can even make the camera clip through the ground below Link and through walls.
It is not required to remove the mask from Link's inventory while in Down A mode. As long as you target while holding Shield, you can still walk around. However, you will not be able to do anything either than walk, sidehop, and backflip. Rolling will cause Link to put on the mask you used to perform this.