Found this stuff a short while ago. I've tested this on the recent PC versions (Eternal, Complete, Chronicles/+); I've yet to test the PSP versions, but it should also work there.

There's more info in the video description, but the first clip can save potentially up to ~8s on the way to the Golden Pedestal, and up to ~20s when getting the Silver Sword. The second clip saves only ~1.5 - 2s to reach the Mine that way if coming from Zepik (early Silver Sword route), so it's probably best not to attempt it for a speedrun. The last clip seems completely useless, but thought I'd show it off anyway.

Anyone else know of other spots with similar transition points that actually carry over your position? I know of a couple places in the SFC version of Ys V, but I don't recall them being of any use.

For the first 2 clips, it's basically making the screen transition at a precise diagonal angle. The transitions usually take place just a short ways away from the visible edges of the screens; essentially, there's a small part of the graphics you normally can't traverse, even though you technically could, if not for the transition points being where they are. So your starting position on the next screen can then end up slightly in the water, or on a rock, cliff, etc. This can be a bit hard to see for the first two spots, but it's fairly obvious for the last one. Basically, I tried to look for what the game considers "corners" close to the transition points, and tried to change screens at said spot.

Once the transition is made, it's a matter of attempting to move further out of bounds, as I've noticed in other games that once you get past the regular boundaries, the stuff normally out of reach can usually be walked on, even if it looks otherwise, since the game doesn't expect you to ever be there. Although in my experience, it's usually hard or impossible to get back inside the regular boundaries once you clip out without abusing something similar to what got you out of bounds in the first place.

For these clips, it's really easy to get back in bounds. You just need to maneuver around the screen edges and move back to where the transition point is. But most other out of bounds instances I've come across have a "wall" or barrier of sorts around the transition point, meaning you basically have to find another clip to reach them from out of bounds. Not sure why that is, as the earlier out of bounds stuff I found for Ys I (viewing Darm Tower, Feena dying at the same point you enter Zepik with her) don't work the same as this stuff on the Plains. I dunno, maybe it has to do with the type of transition point being different.

Well, good luck with testing this! Walking may indeed be beneficial, as it looks like the correct angles to perform the transitions are quite precise. I remember when I was making my TAS, even turning into narrow corridors without bumping could be finicky just because the movement in this game can be ¤that¤ precise.

Looks like someone found some pretty consistent setups for the two useful clips, making them actually viable for a speedrun (albeit at a very small time loss to perform the setup). Here's the video that explains the setups (not mine):

Anyway, I took a look around the remainder of Ys I & II, and couldn't find any other areas that had this sort of screen transition; I could've sworn there were a couple other screens like it between the two games, but I guess my memory's failing. Did you come across anything, Claptor?

The flower one is inconsistent for me, since there's not a good enough indicator of where exactly to stand. The "N" thing is interesting, but I feel like you'd have to commit to mouse movement for a bit afterwards to not waste time (something I don't particularly care for).

I think Kadae's suggestion to tap right is the most consistent, but that isn't 100% foolproof either.

A year has passed and I've only just now found a possible improvement regarding the setup for the clip to the mines. While messing about with some timing comparisons during a stream, I stumbled across a different method for performing it, which has much tighter timing, but is faster by about half a second.

Here's a Twitch clip comparing this method with the old one:

Thank you for that. I'll probably return to attempts sometime in the near future, so hopefully that'll help a little bit.