One of the really cool things about the Super Game Boy adapter - besides the fact that it allowed you to play your portable titles on SNES - was that it added embellishments to certain titles, like two-player modes, additional colours and even attractive borders around the screen. However, there's one title which went even further and actually contained a totally unique game which could be loaded into the SNES itself.
The cart in question is Space Invaders, and YouTube user Rerez has put together the following video explaining why this release is so unique in the Super Game Boy library.
The cart contains a handheld port of Taito's seminal 1978 shooter which runs as normal on the Game Boy. However, inserting the game into the Super Game Boy reveals two options - an augmented version of the standard Game Boy game (as you'd expect from a Super Game Boy-compatible release) and an "arcade version". Picking this results in a loading screen, and when it's done you have a title which is coded expressly with the SNES hardware in mind, boasting improved visuals and better sound.
The port itself isn't particularly noteworthy beyond its presentation, and the basic nature of the gameplay means that it's very similar to the standard Game Boy edition - which might go some way to explain why this release has largely been forgotten about as the years have gone by. Still, it's a remarkable achievement and certainly a unique entry in the Super Game Boy's back catalogue.