Instant Release

Instant release is a glitch where Mario both dives into a grabbable object and drops that object on the same frame. This causes the object to be released before the HOLP even updates, and so the object appears at the previous HOLP. You see, normally while holding an object, the HOLP updates on every frame to the position of the thing that Mario's holding. When Mario releases it, that object appears at the HOLP, causing it to see like it came out of Mario's hands. With instant release, we grab and release the object before the HOLP updates at all, and so the object appears wherever we left the HOLP last.

Not all methods of dropping can be used for instant release. Specifically, the only methods that will work are diving into a wall, diving into out of bounds, diving into a ceiling, and landing with big fall damage. No other method of dropping will work.

Instant release requires diving, and so it can't be used on clones, since cloning involves grabbing (not diving). Furthermore, instant release is a type of drop, and so the released object will appear laterally at the HOLP but at Mario's current height. Thus, instant release is actually pretty restrictive. For example, if we wanted to release a goomba clone or fire clone high up at a specific point in space, instant release could not be used (for two separate reasons).

Additional Notes
(1) For more info on dropping objects vs throwing objects as well as the failsafe mechanism, watch this video:    • Releasing Objects  
(2) For more info on why objects appear at the HOLP, watch this video:    • How Holding Objects Really Works  
(3) For some shots in this video, like when a box fell from really high while grabbing Hoot and when chuckya fell from really high, I used hacks to place those things really high up. That was simply the easiest way to test those things. So don't look too much into how I set up those shots.
(4) I said that diving into an object while sliding on the ground doesn't work with instant release. I tested this more thoroughly than the shot I showed during this statement. Specifically, I tested having a wall appear inside of Mario as he slid into the object, and it still didn't work.
(5) In additional to bonking and big fall damage, instant release can also happen during a big fall into snow/sand.