Hey, I just seen your message! No bother at all, happy to help if I can! First of all, that sprite work looks really nice!
Yeah, it's kind of crazy working with all the tilemaps. The worst thing is palette swaps, especially on sprites. I'm not sure how others work on HD packs, but for me, I started with editing sprite and tile rips, or even maps off VGMaps like these https://www.vgmaps.com/Atlas/NES/index.htm#LittleNemoTheDreamMaster
Here's what my basic workflow was:
0. Optional, rip what you need to rip yourself. PPU viewer has you covered. For me, Megaman is pretty ridiculously well ripped. Little Nemo appears to be as well.
1. Draw the new art over rips. For tiles, this is easier because they're displayed how they're stored, on an 8x8 grid.
- Sprites are a can of worms since they're stored as 8x8, but could be assembled in all kinds of crazy configurations that might lead you to believe they're bigger than they actually are.
- If you are drawing additional details, it looks like it in your preview, then it may be easier to rip directly from the PPU viewer (enable Developer Mode under Options>Preferences, then go to the new Debug menu to find it.) That way you can be sure you aren't going out of bounds when it comes time to insert graphics.
- I looked at Little Nemo and here's some stuff that might help in the PPU viewer.
1. When you open it, you'll see it's showing HUD graphics but not the gameplay sprites and tiles. Change "show PPU data at scanline" to 192 to view gameplay stuff.
2. Seems some tiles show up as black as well, even though their last palette is colored, so uncheck "Display tiles using their last known palette" too, and switch to the various palettes using the dropdown.
- PPU Viewer is also helpful when you run into "WTF is this tile for?" since you can use it to exactly figure out what tiles or sprites are used where and where they are on the dumped sheets.
- You can right click and Copy to Clipboard whatever is display on the PPU Viewer, so if you want to paste that into your editor and edit it directly, it's very easy to do so.
2. Dump whichever screen you want to first. Title, first level, whatever. But just dump that and work on it, I went stage by stage for tiles and as far as sprites went, I would usually dump the graphics each time new stuff came up.
3. Be mindful of when the palettes fade to black, if that occurs at all. Stop recording before that and insert the stuff you've done. Same for fade ins. I find it easier, usually, to dump those AFTER I've inserted new graphics for their regular appearance, because the various shades could end up mixed together on sheets and at least you know where exactly each tile is on the sheet. (Like, each bit of mushroom/ground/Nemo/etc will be on the same tile space of the sheet no matter what* palette is applied, so you can use the original as reference.
- Or you could just skip palette fades. Some games are nuts with those. If your graphics are basically redrawn over the old, the fade out won't be all that jarring. Of course, with really redrawn graphics, then no.
- I copy the normal tiles from the main sheet to the new ones and apply a black layer over them with varying opacity to work with fade in/out, or white, whatever they're fading to.
- *I say "no matter what" but keep in mind, solid color tiles will, by default, be dumped to another sheet. HOWEVER, if you want to use these as extra fade frames**, the FIRST time you dump any solid tile, they will appear with the other dumped tiles. It's only after you dump them again that Mesen will put them into their own sheet. You could just draw a dummy pixel on them if you want, like FFFFFE or whatever, in case you're not sure you might want to edit them later. Otherwise, finding them again on a sheet probably filled with 30, 50, etc copies of that same color is not fun.
- **This will depend on how the game fades tiles or the scenario in which you're working, does it fade them then unfade them again, like in a cutscene or something? It might not fade them and then place black tiles, so in that case, you'd be left with the darkened versions of your tiles, which could actually look cool too! But if you're fading into the next level or menu or something, it will probably change them to blank tiles, so you'll have what appears to be a 100% fade out.
3. This just leaves tweaking the graphics that end up needing fixed or you decide you don't like. I save every single sheet as a project file which I name whatever, like "Stage - Cutman" etc. Well, some sheets I group together, like fade ins and name the layer so I know "Oh, this is for the 75% faded out tiles." Sadly you can't go by sheet number, since that will change throughout the process. If you need to find a sheet to edit again, I find it's easiest to open your project file for it, check the sheet number it used to be so you know it will be that number or larger (it won't go from being sheet 65 to sheet 64, it'll become sheet 66 or stay at 65) (well, GIMP autonames the layer as whatever the filename was you imported, don't know about others, but you could manually name it) then locate it in your file browser, I use the largest thumbnail view and then Photo Viewer to confirm it's the one I need, and then import that new one as a new layer in your project file. That way you've got a more up to date number for the next time you need to find it.
Keep backups of the entire project (like, the actual HDPack folder) each time you know you have things situated where you want them, so if you screw up, like, let's say you dumped palette swaps with your main graphics, ok, just roll back to the last backup.
Also, it seems that once you've edited a tile, Mesen won't move it if it needs to dump another palette of that tile, which would of course occupy the same place. So if you edit the mushroom graphics at their normal brightness, it will force the palette swapped versions onto a new sheet. With this in mind, you could possibly dump each palette fade to its own sheet, by precisely dumping them using frame advance or something, but I never bothered and using the "Slow speed" function makes GUI functions run at that pace as well, so trying to click "Stop Recording" can fail since you clicked it on a... uh, "inactive" frame? I don't know how to word it. Anyway.
Hope that helps! It's still really tedious work I think, but you can definitely get in the groove and it kind of becomes second nature. Still tedious, but second nature haha
I've not used mkwong's editor tool either, since it came out after I made MM1's pack and the other pack I was working on is on hold due to work and life, even though a large portion of it is done outside of actual dumping and insertion. It looks really helpful though, but I never tried it out too much before life/work took over and I was already knee deep in the other pack. Don't wanna rebuild it from scratch, but I might at this rate.
Anyway, I'll keep an eye on this thread, if there's anything else I can help with and I'll try my best to!