"Godzilla vs. Megalon" introduced the cable audience of Mystery Science Theater to dubbed and daffy Japanese monster movies, and I'm tempted to call it a pretty good introduction at that. (I've seen a comment that it's one of the episodes where the series really began to click; it's also the first episode where Joel dons the maroon jumpsuit he would usually wear afterwards.) The movie itself doesn't make a lot of sense, of course, ("Action sequences filmed in Confuse-O-Vision!") what with nuclear testing causing a Japanese lake to vanish, which seems connected to the underground kingdom of "Seatopia" sending forth the monster Megalon, part Christmas tree, part cockroach, and part Chrysler building, who smashes through everything in its path. ("You know, that monster does not know the meaning of the word 'around.'") A robot with a frightening head, Jet Jaguar, is stolen from an inventor, a guy who drives small cars very fast down steep slopes ("Rex Dart, Eskimo Spy!"), and a kid with a very strange dubbed voice who can just be seen to wear a Snoopy sweatshirt. At last, control is regained over Jet Jaguar, who flies off to fetch Godzilla even as another monster arrives sort of out of nowhere, and what seems like the last fourth of the movie is made up of monsters fighting each other. Without much dialogue to talk around, the riffing tosses out huge amounts of fight commentary.
One riff, which involves singing part of the original Japanese theme song for "Speed Racer," has interested me in an odd way. As time wore on, the last few episodes taking on Japanese movies in the eighth season included comments like "please reconsider cartoon gun-toting, big-eyed, prepubescent blondes as your national hero," and people in the "anime MSTing" circles I was in worried that this nastier, somehow less aware edge towards Japan interfered in some way with having the characters knowingly riff on anime fanfics. To be sure, riffing from a position where you think you know it all and nitpick on minor points may not make for the funniest comments ever.