I originally posted about this on the Discord, but I figured it'd be better to have this out there on the open web rather than stuck on a messaging platform that can't be accessed without an account.

The story so far:
I was in Spain and I saw a fake NES classic plug-n-play for sale in between legit NES, SNES, and PS3 consoles. I decided to record video of the entire game list in case it was anything of note. When I got home, I did a rather thorough search for videos of this same console, but couldn't find anything. I did find this video which was close https://www.youtube.com/watch?v=bjUT8XlELuE ...except the one I found had the Mario games switched out (starting with #8 Dr. Mario -> Zooming Secretary).

So without further ado, here's the game list (as pictures because I do NOT feel like typing out all this text):

Sup retro game box 500 in 1 ROM
It works on mame
PC & Android

A few additional hacks sourced from other recent MAME dumps, each of which have some fairly interesting backgrounds:

*Anger Bird 2 (Flipull hack) - This hack originates from the "Play Vision Portable" systems, and was denoted as becoming unplayable after level 4. Going by the ROM itself, this appears to be the result of a poorly-done MMC3 hack; I re-converted the hack's elements to a cleaner MMC3 port of Flipull, thus allowing the game to be fully playable.
*Game Mars of JJ (Super Mario Bros. hack) - A recently-developed variant of Frog Prince that was designed for the "W1 Mini Retro Chick", a handheld modeled after a chicken, for some reason. The hack uses the same chicken as the outer handheld itself.
*Tag Team WWF Smackdown (Tag Team Pro-Wrestling hack) - Generic title screen hack, though it previously appeared on the common 200-in-1 plug & plays with "WWF" ripped off of the title (making it just "Tag Team Smackdown"). I vaguely recall some early 200-in-1 models retaining the WWF logo, though I don't think any dumped revisions retain it.

This may not be the most elegant analysis, but I recently attempted to fix the PCM issue present in games from the unknown set of five 8-bit games (which are speculated to originate from zhengyaxin_8bit). This game set includes Fruit Pig, Eeeck! A Mouse, Echo Chamber, Sudoku, and Trounce; fixed ROMs are provided for the former two.

All of the games in this set repurpose their sound engine from Parasol Henbee; more specifically, they literally copy the entirety of bytes 18010-1C00F from Parasol Henbee (containing all music and sound effects), with no code alteration whatsoever. Seemingly because of this, something within the code results in a bunch of static-like sound coming out of the PCM channel, which is not present in the Parasol Henbee tracks themselves. This is especially egregious in Fruit Pig, in which the entire game sounds heavily muffled.

Further connected to this issue is another oddity; all of the games (save for Sudoku) feature a blank PRG area of 2000 bytes. As far as I can tell, the blank areas are merely intended to mask further PCM output; as filling them with code can further worsen the audio. While I'm not 100% certain on this, I suspect that this is also why Fruit Pig's audio is worse than the others; as its blank area is from 6010-700F, while the other games hold it in 4010-600F. (While entirely unrelated, this also means that the games are effectively only 8K in size outside of audio...)

In Fruit Pig and Eeeck! A Mouse, I was able to reduce the PCM playback by zeroing-out some of the sound channels. There is still some level of PCM present, though it is drastically improved regardless. Unfortunately, this solution did not work for the other games; I was able to reduce Trounce's playback by putting a row of eight "FF" tiles from 4090-4097, though I assume this to not be an ideal code fix (and haven't attached it as such). The sound issue is negligible in Echo Chamber and Sudoku to begin with, so I don't feel a fix is needed for them anyway.

As an additional side note, for whatever reason, Eeeck! A Mouse effectively "plays itself" in some emulators, registering random inputs in-game. Furthermore, Fruit Pig will skip the opening win condition screen, which I suspect is a similar input issue. Both issues miraculously fixed themselves upon muting the audio channels; so that's just an extra benefit, I suppose...

This thread exists to catalog most of the debug stuff I've found in Gamtec games. These range from music/SFX test screens, stage select screens, to debug info shown during gameplay or RAM viewers. These aren't meant to be accessible normally since they're either dead code (not jumped to or called at all) or behind a RAM value that never gets set.

To start this thread off, here's a screenshot of the stage select from Pocket Monsters. This screen also exists in other games made with the Mulan platforming engine (excluding the Donkey Kong games). The text itself is stored in ASCII inside the ROM and is displayed with the Sonic the Hedgehog debug font, which is probably the first time the font ever gets used since its first appearance in the ROM of Tekken 2

You can access it in Pocket Monsters using the Game Genie cheat codes: RE3T-C614+RE3T-C616+RE4A-C6TY+RE4A-C6T0