Two versions marked as "release 1" and "release 2".
The "release 1" disk won't boot without BASIC (revision A) either as a real cartridge in your Atari or attached as an image in your emulator. You can get the ROM here.
Short comparison between the two disks: - the second / later edition will boot on any system - the first version greets you with a "HELLO..." reminiscent of the old Crystalware games (Epyx eventually bought the rights to a number of titles from the company and re-released them, The Nightmare appearing to be one of the projects being worked on at the time) - the directory structure, DOS and the file for one of the booting sequences are different.