Actor Glitch

The name "actor" glitch refers to actors as described in Scenes, Rooms, Actors and Loading. As that page describes, an actor is simply something that Link can interact with, such as an enemy, NPC, grass, water, etc. When you leave a room, the game unloads all actors to save on memory. In some cases, however, we can stay inside the room when the game unloads the room's actors, or enter a room without triggering the load to begin with. This allows for some interesting exploits.

Unloading the Current Room's Actors
This is done by exiting a room so the game unloads the actors as normal, but interrupting the exit so that you stay inside the room instead of progressing to the next. This can be done in multiple ways depending on the room layout.

A common way is to place a bomb at a crystal switch, run to the exit door, and open in just as the explosion occurs. The switch triggering cutscene will interrupt Link and prevent him from exiting the room. However, since you opened the door, the game has already unloaded the actors. This can be done in plenty of places, but one of the most common and most useful is the mirror room in Spirit Temple just before going to the boss door. Utilizing the actor glitch here unloads the moving floor platform, allowing us to fall through and get to the boss door without doing the slow mirror puzzle. A video of this strat follows:
 * At 0:03 we note the chained platform and the sun on the wall. These are actors in this room and will unload once the actor glitch has been executed.
 * At 0:11 a bomb is dropped near the crystal switch and we run to the door. The camera is kept pointing at the bomb for the purposes of the video but that does not matter for the glitch.
 * At 0:15 the bomb explodes and we quickly press A to open the door. Note that if this is done too early, Link will exit the room and the game will softlock.  Too late, and the switch cutscene will begin, preventing you from opening the door.  React to the bomb explosion, don't try to preempt it.
 * At 0:19 the switch cutscene ends and we haven't passed through the door to the next room. The actor glitch is successful, as seen by the lack of sun and chain platform.  The remainder of the video has nothing to do with the actor glitch itself, but shows how the actor glitch is useful in this situation.  Read on if you wish to learn how.
 * At 0:30 we position ourselves in the corner and target the pillar. Sidehop right, backflip, sidehop right, neutral roll and retarget. Backflip, pull bomb in mid-air, and immediately shield-drop it.
 * At 0:38 we perform a right-megasidehop via the explosion. We fall down the hole thanks to the actor glitch and land on a small space on the Colossus statue's shoulder.
 * At 0:45 we turn to the right and move forward a small amount. When Link's head disappears into the statue wall, the position is likely to be correct.  From here we can hookshot the inside of the door to make it to the boss door.  Note that the position is fairly precise. If it is off, the hookshot may bonk directly on the wall in Link's face.

Another means of performing an actor glitch is by use of a crawlspace exit cutscene. When exiting a crawlspace, there are a few frames where the camera remains locked on the mouth of the crawlspace. If a door is opened during this time, the game will load the actors in the next room, and unload the current ones. However Link will remain in the current room. This means of triggering actor glitch is most notably useful in Bottom of the Well in getting bombchus or Lens of Truth early. We can unload the water in the first room, revealing the crawlspace to the Dead Hand fight without the need for Zelda's Lullaby as intended. A video of this strat follows:
 * At 0.07 note the camera changes to outside the crawlspace. Here begins the mini cutscene that is essential to performing actor glitch here.  As soon as the camera changes to this position, a fairly precise position on the analog stick is needed in order to reach the door at the proper time. As can be seen from the input cam on the video, the position is slightly down of the down-left notch.  It may vary a bit with different controllers and mapping, so experiment with your set-up.
 * At 0:09 Link exits the tunnel and turns in the direction of the stick. After a couple frames of Link's turning motion, press A to roll and mash A so you open the door at the right time. The timing for the roll is also fairly precise. An often-used cue is to begin mashing A as a reaction to seeing Link start to move.
 * At 0:10 the door unlocks, but the cutscene prevents Link from leaving the room. We backtrack now to the beginning of the area to make use of the actor glitch.
 * At 0:42 we pass straight through the unloaded water and gain access to the rest of the dungeon.