Sega Genesis? PC (MS-DOS)?

It is the PC (MS-Dos version).

Most of these old games on GOG are. Probably because they are easier to come by and because of DOS BOX emulation.

I sometimes wish GOG got Amiga or C64 versions but understand why they dont. Though there is a good Amiga/ C64 emulator called Amiga/ C64 forever.

I do not think it is as streamlined for making batch files and such but not sure.

It seems to be a solid bit of software though. However, it is commercial and licensed individually. Which would be another reason DOS BOX or emulators like SCUMM-VM are more desirable to use.

I think the first three version of The Immortal were Apple IIGS, Amiga and Atari ST. All three have different music to the NES, DOS and Mega Drive and so I understand the first music was by Douglas Fulton and second by Rob Hubbard, both did other music for Electronic Arts games. As much as a I think Rob Hubbard's music is excellent, I'd like to be able to choose between playing one of the first three ports of The Immortal and the second three, so I can experience both music and there are also some gameplay differences between the ports i.e in the first three, the battle view doesn't change by zooming in on duelists. I've bought a couple of other GOG games that give you a choice between two versions e.g Defender of the Crown, you can play either the Amiga or DOS versions(the Amiga has vastly superior graphics and music, but the DOS version is better in most other ways) and the MacVenture series(Déja Vu 1 & 2, Uninvited, Shadowgate) have a choice between the Macintosh(black/white) and Apple IIGS versions.