Imaginary Friend/WMG

Imaginary friends are actually subconscious memories of former lives.
Cue the horror movies.
 * So in my past life I was a pony? And a butch lesbian Only Sane Man bodyguard with amazing hair? And a plucky chimneysweep? And a Furby? Sweet. (I was a peculiar child.)
 * That means I was a sailor, a convict, a pirate, and a starving Irish girl. Hooray!
 * ...I was every single cast member of Zoom (Optics)... :I (I was an incredibly peculiar child)
 * Oh god yes! I was a eternally pregnant tiger, Peter Pan, and a cloud. And a field of grass.
 * Cool! I was a ninja!
 * And I was a megalomaniacal demon, an schizophrenic half-lizard genius that had ADHD, and a hypersensitive lesbian that could do a Megaton Punch. Huh.
 * and I was a pink hedgehog, a blue rabbit, jerry from Tom and Jerry, a geeky alien (he was more of an imaginary boyfriend), two half human hybrids of a Man-Eating Plant, a talking scooter with obsession to The Hitchhiker's Guide to the Galaxy, a ghost of a rabbit and a littel dargon?
 * So among other things I was a martian named Sally (I got into some Robert A. Heinlein when I was a kid, it did interesting things to my brain), a psychotic lesbian, a dragon, and a tiger? Awesome.
 * Christians seem to think that their Imaginary Friend is God. So does that mean... they are Gods? Now I'm gonna convert to Christianity....
 * This troper's imaginary friend was Faust VIII. Oh dear.
 * An uncharacteristically depressing example: I was an Ill Girl dying of cancer. (What can I say? I could be a real downer of a kid sometimes.)
 * And I was apparently, the letter F, U, and N with eyes and limbs. (...)
 * I was a Cool Horse with magical powers, a purple velociraptor (didn't know how to spell it, sorry), an Affably Evil giant spider, a red-headed kid named Ralph, a crazy fire drake, and a sarcastic-yet-sweet peregrine falcon. Cool!
 * I was a Jewish kid from Venus, Tom from Tom and Jerry, and a penguin. Nice.
 * I was a vampire of the classic Hammer Horror type.
 * Check out the troper tales page for more!
 * So...where does one draw the line? Was every writer ever every one of his/her characters? If so...ooh. What would that mean for the worlds they create? That life's view of it? After the End could be lives at the very start of the Dark Ages...
 * So I was a Polar Bear, and a flying blanket?
 * And I was all the personas I made for myself? Cool... But how can I be the entire Eddsworld gang at once? I bet you'd hate it to if you were a Grammar Nazi. Or you'd find it weird to have been what the third dual bullet first listed. Yes, it's possible for two people to have been one person.
 * That means I was the Genie from Disney's Aladdin! AWESOME!
 * I was Donkey Kong, and an Ailen.
 * I was an entire pack of werewolves.
 * I was Batman and Spiderman
 * I was a robot...

Imaginary friends are actually the result of the instinctive culture of practicing Shamanism, without the symbolic elements
To summon spirits from the otherworld, you need to imagine them first. However, the act of imagining the imaginary friend is actually generating a random spirit from the depths of your unconscious. You have your spirit, but you lack something...

Yeah. the symbols. You generated a spirit, but you have no proper symbolism to make it attach to the real world. So, the spirit will stay as an imagination that inhibits your conscious realm and doesn't have a chance to go to Real Life.

All imaginary friends are real
In another universe, where they have YOU as an imaginary friend.
 * I am accepting this as the truth
 * As do I, but I have a theory/ idea that involves at least two of the both of you. Consider 3 universes (named UA, UB, and UC), in UA, you exist but your imaginary friend is still imaginary, and UC is the same only your imaginary friend is the real one and you are imaginary. UB on the other hand is the universe where both of you exist together (your invisionments of this universe may be in real time, either way they are none-the-less of UB).

Alternatively, many people we believe to be real are actually communal imaginary friends.
Maybe they're granted some semblance of existence through our combined beliefs, or maybe it's all in our heads. A more focused mind could probably identify specific people.

Imaginary friends are alternate possibilities of yourselves
They are the souls that lost out on getting to inhabit your body, and are trying to live vicariously through you to and influence your decisions accordingly.

Your imaginary friends embody certain concepts of you, under certain conditions.
Assuming you stay with and possibly attach memories to them, they may being to embody the concepts or feelings similar to those found in the memory. For example: Connecting one with happy memories will cause the imaginary friend to embody your optimism possibly.