More stuff I noticed.
1. The third Matching Cards game (the one that's unlocked after the second dungeon) in World 5 is unplayable. I checked in the world editor; for the level filename, you entered cardgame1.lvl instead of matchgame1.lvl. It doesn't really matter a lot at the moment because you're able to enter every level infinite times, including the Matching Cards games, the Toad Houses and the Coin Ships. But in the original SMB3,
every level can only be finished once, thus it would be quite a problem if one Matching Cards game wasn't playable.
2. Speaking about the Matching Cards game, there's another issue. You always get the two coin prizes, no matter if you found the two matching 10/20 coin cards or not.
3. (the spoiler contains a spoiler, open at your own risk)
Isn't it kinda boring when the cards in the Matching Cards game are always at the same places?
4. And isn't it kinda boring as well when you always get mushrooms in the Toad Houses and 1-ups from the Hammer Bros?
5. The "9" and "10" level icons, unlike the other ones, aren't animated. Any reason for that?
6. I found two world maps in the world.wld which don't belong to any of the eight worlds of SMB3 or the Warp Zone... (Open the spoiler at your own risk - it might spoil stuff.)

A world that's meant to use the World 4 theme. The level filenames are all left undefined, however.

A world that has no music. All the level filenames are defined; it's probably meant to be an alternative to World 1, as most of the level names begin with "grass". Non-existent levels are king1.lvl (the castle level), grass_game.lvl (the Matching Cards game), grass7.lvl (the level with the "7" icon) and flute.lvl (the level with the "9" icon; probably meant to be the warp to the Warp Zone, also called World 9).
I wonder why they're there?
7. This very pipe here doesn't lead me to the warp level which I went through when entering the pipe at the bottom left corner of the screenshot. Instead, I find myself in the middle of World 7-1, and when I finish that level, I'm still at the same position of the world map where I was when I entered the pipe.
8. The path to this Toad House in World 7 is already accessible before you finish 7-8. The path is unlocked upon exiting the pipe at the very right.
9. The Boom-Boom in the World 8 fortress glitched out of the screen during one battle and I wasn't able to finish the level anymore after that... That shouldn't happen, especially in a world like the Darklands where you need your lives really badly...
Don't get me wrong, I love this remake. But some parts of the remake just don't feel like the original. (But it's probably simply not possible with the limitations of the SMBX level editor. I'm actually amazed that something like the Matching Cards minigame is possible.)