You can save time by catching pendants and crystals in specific positions. For crystals, the way the screen is scrolled when grabbing the Heart Container matters too.
Simply grab it while Link's head is below the shadow of the pendant. This grabs the pendant faster for unknown reasons.
There's nothing more to grabbing pendants (releasing spin does not save lag frames as some might claim)
When you grab the Heart Container in a Dark World dungeon, the crystal's position is set to the center of the screen (not necessarily center of the room). This means that if the room is scrolled upwards as you grab the Heart Container, the crystal will land on a higher position in the room than if it's scrolled downwards.
It is better to grab the Heart Container with the screen scrolled upwards if you can. For Trinexx you have the ability to choose how you want to grab it since it always drops in the middle of the room. Optimally you'd also kill Arrghus at the top of the screen, but most people are more comfortable killing him against the south wall. The difference between a high and a low Heart Container grab seems to be 5 frames overall.
Then we have two conflicting ideas:
- The lower Link is when catching the crystal, the faster it will be catched. Same as for pendants.
- The higher Link is relative to top of the screen (not necessarily top of the room - depends on how the screen is scrolled), the crystal's animation will travel a shorter distance after catching it (before the screen goes black).
As it turns out, it's better to optimize for 2. So what you want to do, in order of priority:
- You want the screen to be scrolled as low as possible when catching a crystal. So walk downwards until the screen stops scrolling. This is the number one priority always.
- After you have reached the lowest scrolling position, the next priority is to put Link as high as possible without scrolling upwards.
There seems to be multiple coordinates that will give you the same fastest time, so you don't have to be perfectly precise to not lose frames. Most people use the crystal's shadow and Link's sprite (his face/hat) for cues that accomplishes this, as can be seen in the link below.
See Michael's science on this, including images that demonstrates good visual cues for catching the crystal. Note that these examples assumes you grabbed the Heart Container while the screen was scrolled up. If it was grabbed at the bottom, you want Link's feet to be above the shadow of the crystal.