Finn is the last surviving human, after the apocalypse. The Great Mushroom War is actually symbolising a nuclear/atomic explosion, which are usually shaped like Mushrooms. The fish people (like Susan Strong,) are believed to be results of radiation from the humans who took shelter in the sewers as the nuclear explosions went off, causing them to attain fish-like qualities. Another sign of these nuclear sightings is in the comic-book, and an episode, where it shows Earth clearly missing a big chunk out of it. Jake had told Marceline that his parents had found Finn inside of a cabbage; which is believed to be the shape of the fall-out shelters the humans used. What happened to Finn's parents, we don't know.
Jake is said to be (a) part of Finn's imagination, or (b) the result of radiation. I believe that he is the result of radiation, as are most of the other characters. Rainicorns are the product of radiation and rainbows. They caused the rainbows in our world to come to life, as unicorns with a pattern.
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Adventure Time Conspiracy Theory
FanfictionThe background story to a show most of us love. I'm entitled to my opinion & this is it, so here you go.
