Find out more about Grizzards here.
If you have an Atari 2600, you can purchase a retail copy, or download a copy for your multicart.
If you don't have an Atari 2600, download the Stella emulator here and the Grizzards files here. Place both the a26 and pro files in the same folder and open the a26 file with Stella to play on Linux, macOS, or Windows.
You'll want these three files to play Grizzards.
These two files must be in the same folder for Stella (or RetroArch) to start up the game properly. Open the a26 file to play, but make sure the pro file is in the same folder.
You'll also want the manual and map file PDF.