Not assembly? Amateurs.

I wholeheartedly recommend everyone try doing a Game Boy game from scratch. The ROM will run on anything. GBDK is accommodating and forgiving. If all you want is some sprites atop a scrolling background, the only obstacle will be remembering to put data into CHR-RAM, so your sprites and background aren't invisible.

Oh they're still using C under the hood whether rustaceans like it or not - games need performance.