Well, after a post in the ROM hacking forum, I determined the only fix for the two tiles in Snowce City is to remove the snow from those two parts of roof. After reconstructing the nearby tiles, I have something that looks acceptable.
Actually, unbelievably, I found a tile editor function in AdvanceMap. I looked up the tile (see image). You don't see it in the image as my screenshot only took the window, but option 00 "???" is off the top of the image. It's already set.
After that and changing the menu below to say "Block is always covered by Hero", I got this image on a ROM reload. It now matches the other tile. I could get this in 413 as well, but to be truthful I climbed onto a rock to get that shot and I'm not changing that movement permission again.
(Apparently, centering is not allowed in VMs...)
For now, noticing no caves back to Route 414 and seeing the size of 415, I couldn't stop myself from backtracking. At this stage, once I'm done mapping Mt. Icestorm (this on an actual playthrough, not backtracking), my mapmaking will be almost done for most of Zhery. Standing in Snowce City and Mt. Icestorm is still blocked off at the south as I didn't play the Gym there yet. :D
EVENING EDIT: I am getting good with the Block Editor now. Fixed a couple more "puddle" tiles in Route 416 (no more silhouettes behind Steam HQ), and fixed the house tiles the Hero refused to hide behind (instead wanting to stand on top of them). I can now wander around town without mysteriously climbing on top of a house. Had to make a second trip when I realized cliff tiles existed with the house tiles on top, but all is working nicely now. I can call Drakebreath City finished in terms of fixes. Fixed Serenity City's name appearance to always show, and checked other cities (fixing one more). I also couldn't stop myself from mapping back to Route 414, but I promised myself I'd stop there. I'm a little flummoxed as to why you can walk up to Diamond on Route 414 (resulting in "...") and he only comes out when you try to walk away from him down the Route - this is going the correct direction, BTW, I hacked a path in to try it out. Shouldn't he hide behind another frozen tree at the bottom of the stairs? Or the script take place before you can walk right up to him?
NEway, going to make one more trip backwards walking on every tile I can access to see what else to fix, and I'll check the earlier areas later (404 and 407 require revisits). A more professional feel when done this will have. Oh, and the 417 hacked in path is removed; I have a save state in Drakebreath on 2 and other backtrack states on 6 and 7 (which I never use), so I figure the path isn't needed now. Hack is currently movement-permission correct as I've seen it so far.
Good enough. Though that would involve sending a ROM...I don't know how to make IPS files. :p
As for the why: perfectionism is in my blood. There could be one tile completely wrong somewhere (I mean completely, not what I consider wrong but still right) and I will change it to what I think is right. It's like a different form of OCD; not the one that Howie Mandel has, as I don't have the irrational fear of germs, but rather I have the need that things always be perfect. The exception is when it comes to cleaning; I know it'll be dirty by the next day, so I don't worry too much about that. :D So in this case, I didn't feel it right that the bases of trees were not visible and wanted them to appear, so I did what had to be done to get them to appear. Nothing changes visually in the play, but it's aesthetically complete if anyone goes into AdvanceMap like me and pokes around.
In any case, I'm glad I went backwards; I've found movement bugs all over the northwest corner of Route 416, and even three tiles above the "forbidden cave" in Drakebreath itself (I'm not going to hack into there either, I am very likely too weak for it). One of those tiles acts like a puddle and shows a reflection. I could mess up movement permissions and do all of 415 and Snowce City as well, but I think I'm better off waiting until I get there as I'm not backtracking through 414 and into Mt. Icestorm, which is currently blocked at the other end.
EDIT: I changed my mind on taking two rows off of 416. First, it meant the stairway was the bottom row; coming off the stairs was the last row on the map. Second, after I tested my modified map with the two blank rows (I made them something I was able to walk under, ironically), I decided the longer look actually is more aesthetically appealing. So I copied the top two rows on Drakebreath's entrance and replicated them (replacing the duplicate sign tile by the entrance with a grass tile nearby) and left Route 416 alone. National Park could use a similar change, actually, but I am not going to go remaking the entire game like this (one because it's not my game and two because I don't want to accidentally screw something up).
If you want to check the map area on the modified string of maps, let me know where to send the ROM or whether you want me to post it on Rapidshare or something. I'll move the guy in the daycare area so you can see what I did (don't talk to the Pokémon, they are not scripted) and you can test the path from 416 (which is now fully mapped) clockwise to 413. I'll fix up any movement permissions I find between the areas (though some "puddle" set tiles need to be fixed; I found some by Team Steam's Base also giving strange reflections) and will also remove the hacked path through the trees in 417. Should check out. There is a house tile that can be trod upon, but I found out the background is different for the one in question; it seems this will require a correction in the tile settings itself. I know the tile can be identified by right-clicking it on the map it's located on in AdvanceMap, and it's just a matter of editing the tile data from there. (See the PM I already sent with a "puddle" tile around cave entrances, verified in two places, and I can get more if needed). If you want me to wait until I'm done playing completely, I can...but that might be a while.
Well, Gym #6 in Serenity needs a blocker like Seanport as well. Right now, I'm wandering around there with no one home. To complicate matters, I don't think saving inside is a good idea; I feel that somewhere a switch will be reactivated and I will become a permanent resident. Add that to your list.
Meanwhile, I'll tinker with some movement permissions; it appears you can walk behind the things that generate electricity and end up standing one square away from the volts on the left or right. That makes no sense, so I'm making those tiles unwalkable.
Meanwhile, hacked into the Daycare area on Route 417. I know you don't actually see beyond that last row of tiles at the top without walkthrough wall cheats or changes to movement abilities, but it didn't feel right having weird forestry there. I've added two rows so I could start the proper row of trees in that area and continued the rest of the tileage from below (trees or cliffs) on either side. Retook a couple of shots to complete that top area on my map so it looks pretty. :D Of course, this led to the map being offset from Serenity City by 2 tiles; I thus had to expand it and Route 413 as well. So far so good; I just have to fix Drakebreath City, and thanks to my temporary path hackin, I can do that quickly (and that's actually the EASY one, I can reassign two rows of Route 416 to the city so as to not extend the path any more than the current version).
The funny thing is, except for a single tree tile from a tree that no longer existed (and the opposite, a tree without its edge, somewhere below), 413 would have looked great in the offset position, perhaps with a small path adjustment.
Once I'm done, if you want to verify that nothing is messed up, I can send you a savestate that can be picked up from where I am now (Power Plant is my next stop); I will leave the savestate on Route 417 and you can walk around the hackin path along the top through the daycare area, or just travel the Route as normal (BTW, I have not battled the Trainers in the savestate in question), back to Route 413. Provided all Trainers operate as they should and no signs are unreadable (I already saved past the script at the start of the city, but I am 100% certain they are placed correctly; everything else is testable), then I can proceed playing from there. Right now I've taken a break to map through to Drakebreath City, and I might try to get 416 before moving on as well so I can just play and write my walkthrough by that point (hey, might push into 415 a little as well); my only mapping complication is the script stairway, which I can change one movement tile to get around to get that last corner. LMAO Obviously I'll have to map Victory Road as well, but at least I'll have a bit of a break in the overworld. Especially with 416. And I already did a rough map of the Victory Road surfing zone for someone earlier today, putting water and rocks in manually, so it's even mostly done.
Actually, I knew Water moves were boosted too; I just said Electric in general because someone in the hack mentioned Thunder (if it's only Thunder, I have Thunderbolt instead). The Solarbeam halving I actually did not realize as I dislike two-stage moves and tend not to use them.
So yeah, I guess I am making my life more difficult. I OHKO the Huntail and Gorebyss, so no change in difficulty there; meanwhile, I have no Fire with me and the one I'm about to face will not be hindered due to no rain; Remoraid, Wartortle, Poliwrath, and Octillery should be OHKOed. Guess it's not doing much to me on this Route if I left it on.