Adventure Time has become an increasingly popular show as of recently, garnering a massive following amongst both young and old alike. The story details the misadventures of Finn, and his anthromorphic, magical pug, Jake, inside a world filled with weird, wacky, and often somewhat humourous things.
But, there is always something that just seems odd. Something dark about this cutesy little world that few people ever pay heed to. Don't worry, this isn't some bullshit theory about "It's all in Finn's head," or "He's autistic/ batshit crazy/ in a coma," but the truth just so happens to be much darker. It isn't another world, or Purgatory, no...
Finn and Jake are living after the end of the world.
Before you try to say "Bullshit!"... Just think about it: Finn is practically the only human in existance, everyone else just so happens to be oddly proportioned, or miscoloured, or awkwardley tall or short. The explanation is quite obvious.
Mutants, the remenants of humanity changed by a massive, energetic, and possibly magical force. This very same force is what made the "Candy Kingdom", or, at least it made its inhabitants by possessing a large amount of inanimate objects, not only bringing them back to life, but also making them entirely sentient, giving them their own personalities.
This let the cartoonists develop some humourous and adorable references to other series, suh as World of Warcraft, or Futurama, but that's beside the point. In one episode, just as well, Finn claims that "rockets weren't re-invented yet," meaning Finn may be somewhat aware that there was some significant event happening at some point before the show's main plotline.
Remember the episode where they descend into Marceline's memory, or where they discover a troglodyte-like society under ground? Both these episodes have modernistic, yet destroyed cities in them. Some people even claim that in the former episode that gunshots, screams, and explosions were to be heard in the distance during the sequence. However, the landscape of the world was significantly changed, meaning some sort of magical force not only morphed the people, but the landscape, alongside a massive war.
In the latter episode, during the end, the "humans" are revealed to be mutants, with odd, fishlike appendages sprouting from their heads. So far, these are the least mutated humans to appear in the series (aside from the frozen businessmen, who were likely, aside from Finn, the last "true" humans on Earth.) Finn appears to be shocked by this, meaning he is somewhat naive about the truth of whatever event shaked and changed Earth.
Here's a more formulated theory that I have come to accept, and, so have many others alongside me.
At some point in the distant future, a war broke out over resources in the world. As countries began ruthlessly bombing and fighting each other, drilling and mining not only continued, but increased, as nations began competing for the world's last remaining reserves. One of these expeditions uncovered a massive, magical energy base that been trapped within the world for millions of years. It spread quickly, morphing and changing the landscape, bringing random objects to life, and mixing with the already copious amounts of radiation that had mutated so many people. The magical energy canceled out the radiation's effects, but enhanced the mutations, allowing the odd "humans" to increase their numbers. Finn likely came from one of the last remaining human settlements, the lone survivor of an attack by the many marauding mutant tribes in their world. Found and raised by dogs (well, talking pugs, to be specific), he was raised as one of their own to be a great hero, and avenge his human ancestors.
Remember next time you're watching Adventure Time to think about the dark secrets the show actually holds, and how so many moderninstic things can exist in such a medieval, fantasy-like society, and why exactly is Finn the last human there.