Bizarro (also known as Bizarro Fiction) is a relatively new genre, characterized by how bizarre the works, generally in written or film format, really are. However, it is meant to not only be strange, but also of quality. It is meant to raise questions as much as eyebrows.

"Bizarro isn't just weird fiction, it is DAMN GOOD weird fiction."

It often falls somewhere somewhere between/inside the categories of horror, scifi, or fantasy, and can usually be described as "weird cult fiction". Being weird in itself is not especially new, and neither is being weird to make a point about something. What this brings, though, is a place to put these strange tales. Alice in Wonderland or the film Eraserhead serve as sort of base for these to elevate from.

Bizarro differs from such things as experimental fiction in that it is not the styling of it that is weird, but the plot. Take, for example, The Egg Said Nothing, which reads like any other book, but the storyline is about a queer man who laid an egg in his sleep.

But then, what is the difference between it and just plain science fiction or fantasy? Well, those generally have one strange item. However, if you were to add more to this, it would certainly become bizarro. A perfect example:

Jurassic Park – the weird element for this that makes it science-fiction is that it is about a zoo for dinosaurs. So to add another weird element, I’d change the characters from a nice family of scientists to a group of pornographers who have broken into the park in order to film bestiality fetish porn with the dinosaurs. For a third weird element, I’d make it so that the act of having sex with these dinosaurs somehow gave the porn actors super powers. Right there, the story would be weird enough to be labeled bizarro. I’m not sure if it would be any good, but it would be bizarro.
- stolen from here

It is a very close community, as may be indicated by the recommended links.

References:
Bizarro Central
Specus Sphere
the Wiki
Mondo Bizarro Forum

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