Weirdworld (later changed to “Warriors of The Shadow Rhelm”) was created by Doug Moench and Mike Ploog and first appeared in the black and white magazine Marvel Super Action #1 (January, 1976). This tale from Marvel Preimere #28 (1977) is the 2nd of 1st three tales illustrated by Ploog, and the only one inked by Alex Nino. The whiplash-inducing ending suggests that the creators had their original page count for the story chopped at the last minute.
Weirdworld kicked around a variety of Marvel titles between 1976 and 1982, and one of the swamp serpents even made a cameo in X-men First Class II (2008). The three part mini-series in Marvel Super Special, illustrated by John Buscema, was heralded at the time for its use of full color paintings throughout. Although Ploog and Nino have very different art styles, they mesh surprisingly well in this story. This is a series that would benefit from a good collection, with an added tale or two to finish up the story.
Tim Perkins has a nice overview of the series and features some of his own unpublished “Weirdworld” art.
Lots of information about Weirdworld here.