Among other offbeat, obscure comics I've come across recently, some years ago I was intrigued by mention of an underground comic that was a sequel to a single-issue of a "weird menace" pulp, The Octopus, published in 1939. That had been an attempt by Popular Publishing at a "villain pulp", where the main star was a villain similar to how the "hero pulps" had main stars like The Shadow, The Spider, Doc Savage, Secret Agent X, etc. The Octopus being a mad scientist sort who wreaks havoc in the city. Their previous attempt at a villain pulp had been a short-lived magazine about a Yellow Peril character, Dr. Yen Sin. Popular also published what turned out to be another very short lived attempt at a villain pulp soon after The Octopus, The Scorpion where they just swapped out a new mad scientist/cult leader for the Octopus.
Now, in the 1970s there'd been something of a pulp fiction revival, what with the paperback reprints of hero pulp characters like The Shadow, Doc Savage, etc, small press reprints of "weird menace" pulps, detective pulp anthologies, Western pulp stories, etc. One editor, Robert Weinberg, had published reprints of The Octopus/Scorpion etc.
So from a underground publishing called Pulp Mania came a comic with typical weird underground psychedelic comic art that was a direct sequel to The Octopus, "The Skull Killer", where the masked vigilante who challenged the villain originally, the aforementioned Skull Killer has another go-round. I'd seen copies of it around, but only really looked into via a blog that posted pages.
Goin' Underground: The Skull Killer (Pulp Mania Inc., 1975)
It appears, despite promising a follow-up with a Nazi villain, there was only one issue because the people behind it, a writer named Brendan Faulkner and artist Gary Terry thought the copyright on the character had lapsed, but it hadn't at the time. Oops.
Artist Terry, who when I looked into him had a career that involved very little comics work but a lot of animation and storyboarding. Sometime after Skull Killer, he published what was supposed to be, again, the first issue of a digest-sized, black-and-white comic book,
Atom Robot Adventurer, which featured a manga-inspired story featuring the titular character that came off like an adult riff on Astro Boy and a saucy, kinky attempt at revamping obscure WWII-era comic hero The Green Turtle, and ads promising more titles coming in 1976 that it looks like never came to fruition.
Atom Robot Adventurer