> Did you know it was possible to create a GBC cart that would act as a fully-fledged SNES game (i.e. mapping a separate SNES game ROM) when plugged into a SNES through a Super Gameboy? Or to have “progressive enhancement” logic in the GBC ROM itself that draws full-color sprites (OBJs) when played on a Super Gameboy? AFAIK, literally nobody has ever fully exploited this, not even demoscene devs.
Fully exploited. Space Invaders was a partial exploitation at best. It was just a tiny stateless SNES ROM-image, that got loaded from the GB cart's ROM into the SNES's tiny work RAM, and then executed from there (leaving approximately zero WRAM for actual gameplay state. Good thing it was Space Invaders!)
A full exploitation, IMHO, would look more like the thing Pokemon Stadium did with Pokemon RBY — but done purely in-cart in the GBC game. A SNES game that "interacts with" a GBC game through the SRAM, such that you're playing the same game, two different ways, when you put it in your SNES vs. when you put it in your Gameboy. (Pretty much like Dragon Quest XI Definitive Edition's ability to reboot the game between 3D and 16-bit mode.)
Of course, to do that, you'd need actual separate ROM chips in the GBC cart for the SNES game, so that the SNES ROM-image could be larger than WRAM yet still fast. All that ROM would be untenable to fit into a GBC-cart sized cartridge even in 2003, the last year of the GBC's lifetime. It'd be perfectly doable now, though!)
One game did! Space Invaders, of all things. Jeremy Parish did a video about it: https://www.youtube.com/watch?v=GAyt8NI9u9c