While we see prototypes for the original NES pop up, it’s not often we see one for the Super Famicom surface. This one is for the Super Famicom version of Sonic Wings (Aero Fighters in the US). This cartridge was sent to Waldmeier AG, the Swiss distributor of Nintendo in August 1993 for evaluation.
The seller has a 172 feedback score with 100% positive feedback. The current asking price is $350.