Let's talk about The Valley of Death
Trap 18 is the most dreaded part of the game, because it depends on luck that is mostly unmanipulable. Like any trap square, you need overworld enemies to run into Link as he is walking onto the trap square in order to overwrite the forced encounter with a shorter random encounter.
You need the same thing at Trap 17, but that one is easier to manipulate. You can keep creating extra delay frames during the walk from Trap 16 to Trap 15 in order to change the random enemies that appear in the graveyard between Trap 15 and Trap 17. Eventually, you get a result that works. The result that I got lost 2 frames compared to the current movie.
However, here's why the Valley of Death between Trap 17 and Trap 18 is so notorious. You have to deal with 3 sets in a row of 3 enemies that you cannot change with overworld movement delays. And you get only one step down to avoid an enemy that appears in front of Link.
Look at the TAS history (6 movies) of this part:
-The first movie completely gave up and accepted the forced encounter
-The next two movies entered and exited the forced square and then waited for enemies to spawn again.
-The fourth movie was the first to actually get the random encounter, after taking a bit of a winding path.
-The fifth movie looks like a downgrade, walking backward at one point.
-The current movie is super lucky, basically.
But I found that you don't have to completely accept the 3 sets of 3 enemies that you're handed. You can create delays at Trap 15 and Trap 17 to change the timing. But, it's limited. In my case, I was limited to only 6 possible combinations:
-Delay Trap 15
-2x Delay Trap 15
-Delay Trap 17
-Delay Trap 15 & Delay Trap 17
-2x Delay Trap 15 & Delay Trap 17
Any additional delay at Trap 15 changed the enemies in the graveyard to an unusable grouping. So I was limited to testing these 6 options. If you get a set of enemies that surround Link, you can pretty much forget about using that option at all. So I narrowed it down to 2 options that actually had a chance of working.
The first option decided to throw in yet another degree of difficulty by not letting enemies rise up from below Link. And nothing is coming from the left, leaving the top as the only possibility. Nothing worked.
Fortunately, after many hours, I found that there was one way to make the second option work without an ugly winding path. It still lost 27 frames. But, if that last option hadn't worked, I would have been faced with much greater losses, probably in the 60-90 frame range. So, despite losing frames here, it's the best possibility of a bad situation. It won't look bad to the casual viewer. I topped out at 396 frames ahead; down to 367 now.