[[caption-width-right:350:SnarkBait? You bet.]]

->''"You may come from beyond the moon,\\
But to me, you're just a goon!"''
-->-- '''The Other Three''', lyrics to TitleThemeTune

In 1965, director Creator/HerschellGordonLewis needed another movie to round out a double-feature with ''Moonshine Mountain''. So he bought Bill (''Film/TheGiantSpiderInvasion'') Rebane's unfinished ''Terror at Halfday'', added a couple of extra scenes, some new dialogue, some narration, and voilà: ''Monster a-Go Go'' was born. (The birth was illegitimate, as Lewis did not deign to put his name on the movie, instead crediting himself by the pseudonym "Sheldon S. Seymour.")

The plot, such as it is, is that an astronaut has gone missing after crash-landing in suburban Illinois. At the same time, a monster that looks suspiciously like the lost spaceman (and is highly radioactive) has been terrorizing teenagers and scaring the pants off of the locals. Scientists work to study the monster, but he escapes into the UsefulNotes/{{Chicago}} sewers, only to disappear suddenly.

For the ''Series/MysteryScienceTheater3000'' version, please go to the [[Recap/MysteryScienceTheater3000S04E21MonsterAGoGo episode recap page]].

!!This film provides examples of:
* AlanSmithee: Herschell Gordon Lewis is credited under the pseudonym of Sheldon Seymour for his writing and producing roles. He also takes credit as the film's production designer... under the name of [[SdrawkcabName Seymour Sheldon]].
* BlatantLies: [[UnreliableNarrator Anything the narrator says.]]
* CosmicHorror: Maybe? As with so many things in this movie, this is never elaborated on.
* DreadfulMusician: The composer/musician of the actual score (who is uncredited, perhaps due to shame). To elaborate, the score consisted mainly of sparse, jangly {{Scare Chord}}s played on a Fender Rhodes and amplified to distortion; it's atonal, harsh, and probably meant to be creepy, but just gets annoying after a while.
* GainaxEnding: [[spoiler:There was no monster.]] This chain of events is also never explained properly, making what was supposed to be a ShockingSwerve turn into a huge PlotHole.
* {{Jerkass}}: Dr. Carl. Talks to the wife of the mission's pilot about how well a mission went when ''the pilot didn't come back alive'', instructs a mother not to tell her son that his stepfather is dead, and inexplicably disappears before doing anything useful. And he promised the kid they'd go out for milkshakes before vanishing while the kid is out of the room. Considering the quality of this movie, vanishing from it might make Dr. Carl a KarmaHoudini.
* LastNameBasis: The Logan brothers.
* MindScrew: How the climax happened is not only never explained, but {{handwave}}d by the narrator at the very end.
* NeverTrustATitle: There is a very very ''very'' brief moment of go go dancers at the very beginning, but you have to imagine anyone not making out with their girlfriend at the drive-in felt profoundly ripped off.
* NothingIsScarier: Used very poorly. Nothing at all is, it turns out, a huge letdown.
* PlotHole: Plenty of them, due to the incomplete nature of the film. Very little of what's going on is explained properly, and attempts to explain it just end up posing more questions than they answer.
* SpaceClothes: On the monster. Inexplicably.
* WhamLine: [[ShockingSwerve Not in a good way.]]
-->'''Narrator:''' As if a switch had been turned, as if an eye had been blinked, as if some phantom force in the universe had made a move eons beyond our comprehension, suddenly, there was no trail! There was no giant, no monster, no thing called "Douglas" to be followed. There was nothing in the tunnel but the puzzled men of courage, who suddenly found themselves alone with shadows and darkness! With the telegram, one cloud lifts, and another descends. Astronaut Frank Douglas, rescued, alive, well, and of normal size, some eight thousand miles away in a lifeboat, with no memory of where he has been, or how he was separated from his capsule! Then who, or what, has landed here? Is it here yet? Or has the cosmic switch been pulled? Case in point: The line between science fiction and science fact is microscopically thin! You have witnessed the line being shaved even thinner! But is the menace with us? Or is the monster gone?
* WhatHappenedToTheMouse: About half the characters disappear about halfway into the movie. One of them, Dr. Logan, is replaced by his brother, Dr. Logan, who is the same actor with a different haircut. The reason for this is because Lewis attempted to complete the film several years after Rebane abandoned it; the new characters replace the old ones whose actors were unavailable, and the same actor playing his original character's brother was on account of the actor being available but having drastically changed his appearance in the interim.
->As if a switch had been turned, as if an eye had been blinked, as if some phantom force in the universe had made a move eons beyond our comprehension, suddenly, there was no Wiki/TVTropes page.