I use a reverse engineering tool called Ghidra to analyze memory snapshots from flycast. I've come up with lots of previously unreported cheat codes this way, including some for Rayman Saturn.
I've been poking around in the Dreamcast version of Rayman 2. I found a cheat code that seems to be unknown. The game checks for it the same way it does the "random textures" and "change VMU icon" codes. You can enter it on controller 2 at any point (except during the auto demo), but you have to...