itch.io

I haven't tested it on RetroFreak in particular, but looking through their firmware updates, I'm not sure their NES emulator has received significant updates since 2016 (I could be wrong); it's very possible it doesn't support mapper 30.  The majority of modern NES emulators should give you no issues running Zed and Zee unless they're based on old code.

It seems like John NESS doesn't support mapper 30, which is used by a lot of aftermarket NES games (including Zed and Zee).  I tried that emulator with another mapper 30 game and received the error you described.

RetroArch is free on the Google Play Store and includes multiple emulator options that work with mapper 30 games like Zed and Zee!

There are six worlds with six levels and a boss battle each, so 42 total!

Thank you!  Love seeing the Tengen all-stars here!  Even though we're not officially related to the original company, we hope our work honors the Tengen legacy as we forge our own new path.

Zed and Zee has been tested and confirmed to work in an Everdrive-N8.  It hasn't been specifically tested in the Pro model but should work!