The stories running through issue #12 of Man-Thing (from 1974) and issues #1-3 of Infernal Man-Thing (2012) are collected, along with the Man-Thing's origin story from issue #1 of the magazine Savage Tales (1971), as Infernal Man-Thing. The story from the original Man-Thing comic is `Song-Cry of the Living Dead Man', and the Infernal Man-Thing story is a sequel - `Screenplay of the Living Dead Man', which although written in the 1980s (according to Ralph Macchio's introduction), and assigned to an artist back then, was only completed by the artist fairly recently after an editor found it was still `ongoing'.
THE SPOILER ZONE The original Man-Thing comic book was basically a vehicle for Steve Gerber to write anything he felt like; and Jim Shooter has described him as being the best writer to ever have worked in comics - but not necessarily the best comic-book writer. I was a great fan of the Man-Thing comic book back then, and considered it one of the best comic series ever published. I am much older now, and have bought a copy of the Man-Thing Omnibus to see if it and I have survived the test of time. `Song-Cry of the Living Dead Man' was a story that went over my head - being slightly Autistic, there are probably many themes that pass me by, and it wasn't one of the memorable stories for me. It is a tale of a man (Steve Gerber) having an existential crisis that manifests itself in the real (comic-book world). None of the personal problems that afflicted the character ever affected me - one of the benefits of Autism and a god job in IT- so I could never relate to it. The sequel story, `Screenplay of the Living Dead Man', picks up the original story ten years or more after the original, and goes over much of the same stuff, but with ten years or more of personal issues that needed to be dealt with. If you liked the original, then this is a development, or sequel to it. The artwork however was not in a style that appealed to me.
The origin story is a black-and-white story from Marvel's first attempt at a comic for `mature' audiences, but the story is still a very interesting one, with good scripting and artwork.