Did I just discover a secret in Sonic CD USA version? Has anyone else done this?

This is actually used to unlock a secret in Panzer Dragoon II: Zwei. Soft reset to the bios with an Azel: Panzer Dragoon RPG (Panzer Dragoon Saga) disc in, take it out and insert your PD II: Zwei disc and the intro to the first Panzer Dragoon game will play and you'll unlock a secret level in your Pandora's Box. Granted its just level 2 in ultra tiny screen mode but it stays permanently unlocked after doing so.

 

Wow, I didn't know about that. Something to try over the weekend me thinks

 

As far as I remember, the Sega Saturn A+B+C+START was "required" for game approval. The developers needed to include the code supplied by Sega. It's in some dev manual. It's a system shortcut.

The Sonic CD shortcuts are game shortcuts. I believe another one with shortcuts like that is Pitfall - The Mayan Adventure.