The mirror universe is definitely an example of "space fantasy" - i.e., fantasy that happens to be set in space, where the "magic" is styled as pseudoscience but is still just magic. The difference is one of jargon. Harry Potter says expecto patronum; Doctor Who says reverse the polarity of the neutron flow. In both cases, the spell works because a fictional law of nature allows it to. There's a continuum between space fantasy and sci-fi. Doubly so because our understanding of science deepens over time, and yesterday's speculation resembles mere whimsy now. For instance: the earliest text to be described as "sci-fi" dates to the second century, and features people being blown to the moon by a whirlwind. I think space fantasy has been part of Red Dwarf since day one. Timeslides and the mirror universe are cut from the same cloth, but Timeslides isn't the only "golden age" example. In science terms, the plot of Confidence and Paranoia is utter nonsense. "Pneumonia" is a symptom of many diseases. It isn't an organism and can't evolve. Even if they'd used a specific pathogen, how would hallucinations manifest themselves as flesh? Where does the matter come from? How does it organise itself? There's also Backwards and Parallel Universe. Like the mirror universe, these settings have inconsistent logic. The priority is to drive the plot and supply humorous set pieces. The writers didn't reverse a single variable and project plausible outcomes. It isn't scientific speculation and ceteris paribus doesn't apply. The backwardness of Backwards is all over the place, and there's only a visual punchline (and proverbial logic) to justify Cat getting a dog for his counterpart. Other episodes have elements of space fantasy too. Scientifically speaking, why would a triplicator distil good and bad elements based on human conventions - like edibility and empathy? A metaphor can link rotten food to cruel behaviour, but the story suggests there are laws of physics to link them. This is basically why I felt Only the Good was business-as-usual, when a lot of RDVIII wasn't!