Okay, this might be a long one. I've been looking into something probably not very many people are aware of, in this age of emulators and whatnot (especially when some of the games it concerns are damn near impossible to find in cartridge form): the dubious phenomenon of .. custom gameboy boot logos!
So, a brief explanation. For a piece of software to run on a Game Boy, it must contain a copy of Nintendo's logo identical to the one in the console's internal ROM, and that logo will be displayed at startup; this was presumably done for similar reasons as Sega's TMSS, in that it forces any unlicensed producer of cartridges (whether a pirate or an otherwise legitimate unlicensed developer) to include the Nintendo logo in their games, theoretically committing trademark infringement in the process. These measures were particularly aimed at Taiwan, which at the time had no copyright agreement with Japan but did allow Japanese companies to register trademarks; this is why you'll often see Taiwanese pirate games with company and console logos removed but everything else intact. (It's also one of the many reasons NTDEC - Nintendo Electronic Co - ended up with a massive lawsuit from Nintendo, while its competitors mostly escaped.) But, fortunately for unlicensed developers, Sega's TMSS didn't hold up in court (in the US anyway), which I'd guess rendered Nintendo's Game Boy efforts largely pointless too.
Some companies, though, (whether they believed it legally necessary - which it may well have been in some places - or they just wanted to stick two fingers up to Nintendo) managed to replaced Nintendo's logo with their own. This works because the Game Boy reads the logo twice: once to display it, then again to check it against its own stored copy. So the cartridge provides the custom logo for the first check, then Nintendo's for the second - you can see this being exploited in this video. The Game Boy Color performs the check differently, which breaks older mono games using this method (eg Sachen's) but only checks the first half of the logo, hence why you'll sometimes see GBC games that only modify the lower half. Others still managed to replace the whole thing, though. Inevitably the GBA came along with yet another modification to the checks, but every GBC game I've tried seems to sidestep this by feeding it the standard Nintendo logo.
Now, emulator users will probably be unfamiliar with all these logo shenanigans; the GB's internal ROM was only dumped recently, and even those emulators that do make use of it (such as MESS) don't emulate the hardware trickery employed by these carts to display a custom logo, so you'll only see Nintendo's in any case. But the alternate logo is, usually, still present in the ROM at 0184h (sometimes accompanied by an entire secondary header, sometimes just the logo itself); if you use a hex editor to copy 30h bytes from that location over the real Nintendo logo at 0104, you can see the custom logo in any emulator that would otherwise display Nintendo's. Even if the game won't boot.
Anyway, I've tried this on pretty much every unlicensed Taiwanese/Chinese GBC ROM I could get my hands on, and here are the logos I found:
A Taiwanese unlicensed GBC developer. This logo appears in most of its GBC games (the mono GB ones were by different people entirely, and the current ROMs are cracked in any case). "Most", because some of the later ones have...
This! Top half Nintendo, bottom half Hot Kid (which was a brand name used by Gowin sometimes). And they so nearly pulled it off, too.
Another Taiwanese unlicensed developer - the makers of Shi Kong Xing Shou, which I dumped recently. Aside from the games explicitly credited to VF already, this also appears in Rockman DX3 (Zook Hero 2), some Three Kingdoms game (in GoodGBX it's "Shawu Story", but some of the alts are a different game entirely) and Super Fighter S ('99). The first two were pretty much already known as VF games anyway, and Super Fighter S was kinda speculated to be one based on leftover graphics in their other stuff, but hey its nice to have confirmation.
Only used in Soul Falchion, which is also pretty much accepted to be a V.Fame game .. wonder why they didn't use their own name, though?
Waixing! A fairly prolific NES developer, but next to nothing is known about their GB stuff. The only game I found with this logo is "Legend of Heroes", which doesn't seem to boot in any emulator.
An obscure one, this - try searching for it. as of this writing there's only a smattering of spam, OCR errors and GBC roms misinterpreted as text. Appears in E'Fighter HOT, Garou: Mark of the Wolves and Dragonball Fight 2005 (a title hack, not sure what its real name is). All fighting games based on Takara's GB KOF engine.
Okay, I don't have a screenshot of this one. But Sachen used custom logos too. Yep.
The developer credited for quite a few GBC Sintax games. This particular logo shows up in Harry Potter and some versions of Metal Slug 2001.
First encountered in "Final Fantaxy IX", which I own, and am currently trying (and failing) to dump. Also used in "San Goku Shi - Act C" (rom name), which also happens to be called "FF9" in its fake header. Hmmmmm.
From "Zelda Shi Kong Zhi Zhang", which is encrypted, so I have no idea what it is. The header name is Digimon, though, so it could be a reference to that rather than a company name.
And we're onto the cheap edits of the Nintendo logo. Woo. This one is in "Bokujou Monogatari GB2 (Unl)" (that's the rom name; its nothing to do with Harvest Moon really, I'm not sure what its real name is), "Dragonslayer Chapter - Surrounded" & "Sky Dragon" (again, rom names), Harry Potter 3, "Heroic Sword", one version of Metal Slug 2001, and one version of Final Fantasy X: Fantasy War. Doesn't seem to be a great deal connecting these games; maybe a few different developers used this one?
Christ. Really? Yeah really. Yiutoudz. Appears in another version of Fantasy War, and King of Fighters R2. These were both at least published by SKOB (and its fantastically named Chinese affiliate "Super Huge Dragon"), but other SKOB games seem to retain the Nintendo logo.
I don't think this is supposed to be anything. It's just not supposed to be Nintendo. But it still pretty much is. Ah well! Mostly, if not exclusively, used by Sintax, it would seem, in the likes of "Castlevania EMO Demo" (rom name), "Saishuu Gensou" (rom name again), Shin Sangokumusou 2, Zhong Zhuan Qi Bing, Ice Age, Ice Age II, and Pokemon Sapphire.
As far as I'm aware, Yong Yong games (ie the characteristically awful ones) don't have custom logos, if you were wondering. Or if they do, I can't find them, and I don't care about Yong Yong enough to look. And that's that! Maybe.