I thought the GBC version Unseen64 shows was ruled out as a hoax. Or was there a canceled prototype that Nintendo was planning on releasing at one time?
GBC version had a legit announcement from Nintendo (like Metroid 2, Mega Man V, Densetsu no Stafy...)
It was Kaeru no Tame ni Kane wa Naru DX.
Anounced around 2000~2001.
Slated for February 2002, 3800 Yen, back-up memory and all.
The very cheap yet more powerful WonderSwan Color came and the GBA was rushed to the market (kind of like DS was in response to the PSP in 2004), and as a result Nintendo cancelled a ton of GBC/IR-addon projects, including this game.
So in the end only the Nintendo Power 2000 rerelease of the monochrome original happened.
However what's established is that none of the four or five screenshoots circulating in most Western (and even Japanese!) coverage of the DX version's announcement originated actually from Nintendo (aside from the title screen which is the only one technically possible with the GBC's palette limitations, though not proven to be legit either).