With these issues, the cover gets a tagline: The Most Startling Swamp Creature of Them All! I’m assuming this is because Len Wein, creator of Swamp Thing for DC, now works for Marvel, and they’re trying to compete. I doubt it has anything to do with Marvel’s own Glob.
Two really old people have moved into Man-Thing’s swamp. The wife gets sick, and in her anguish she accidentally brings a demon in to haunt the swamp. Meanwhile, her husband is leaving the swamp to get her medicine, and Man-Thing protects him from the evil mojo.
In the end, the old man’s dog-who his wife always hated-dies killing the demon. The husband and wife get the last word, in the pictured panel.
Creators: Steve Gerber, Mike Ploog