IMHO SGB would be out since that would be a GB game, but any special controller would be fine. Emulators support those, new SNES mice are being sold, etc.
Viewing post in Making a SNES game that works only with a SNES accessory?
Thanks for your answer. And how about a SGB game that would use SGB only features? (like colors, SNES sounds, multiplayer, etc.)
There is some untapped potential in this accessory IMHO, as most commercial SGB games didn't rely on the SGB-only features to be able to work on a GB too. But I've been tempted to make "SGB-only" game for quite some time, that compo would be a good opportunity to finally try my hand at such a project if it's not against the rules?
In the gameplay idea I have in mind, the code will mostly run on the SGB CPU indeed, but the input, and audio and graphical output will be SNES related. I know it's kind of a stretch, but I see it quite similar to using a SA-1 chip or SuperFX chip, which the compo rules allows. And the fact to use an accessory like the SGB is tied to the "perspectives" theme :).