Dallan and Sepsis, that's a cover!

It's entirely possible that I buy this every time I see it in the quarter bins, but it's a stone classic: from 1979, the Micronauts #7, "Adventure into Fear!" Plot and script by Bill Mantlo, plot and breakdowns by Michael Golden, finishes by Josef Rubinstein. 

The Micronauts were still trapped on earth, staying with their young friend Steve Coffin, whose dad Ray had fallen into the Prometheus Pit, a gateway to the Microverse. After a Star Trek rerun, they catch a news broadcast noting Project H.E.L.L. was still sealed off by a force-field, but not mentioning Ray or any tiny aliens. No one knows that Ray was currently having a conversation with the mysterious Time Traveller; but Steve was distraught, and strong emotions in a Florida swamp...you know what that means: the macabre Man-Thing! Cementing the Micronauts in the Marvel Universe! 

Steve is understandably, pants-crappingly terrified; while the Micros are mildly concerned, what kind of planet was this? They have a hard time doing any damage to the swamp monster, so Steve fires up the airboat, chopping the Man-Thing into slimy mulch! Oh, he's fine. While not being aware or sentient, there's still the sense the Man-Thing kinda threw that fight, rather than hurt the kid, and gives him the win he needed to keep going. The Micronauts regroup, to begin their search for Ray and a way back to their battle with Baron Karza...not realizing, the Baron was now arriving on earth! 

Even if you somehow weren't reading Micronauts at the time, you might recall this one, since there was a full page house ad for it.