
I made this as a quick guide for those who want to play with OUaT characters, but are concerned about knowing their canon backgrounds.
( In General )
Once Upon a Time is an urban fantasy show about a small town, in modern-day Earth, called Storybrooke. Storybrooke is a typical small town. Everyone in the town has lived there for as long as they can remember, and they're either inclined to live out their whole life there or else fear leaving it for reasons they can't explain.
The truth is... every single person living in Storybrooke is a children's fairy tale character, who have been transported from their land of magic (Enchanted Forest) by an Evil Queen (Snow White's Stepmother) via a curse. The truth is, the curse erased all memory from the citizens and replaced them with ones that make sense according to their new environment, though a lot of their mannerisms have transferred. They instinctively don't feel right about leaving Storybrooke because they can't. Those characters that have crossed the town lines have gotten into terrible accidents.
The curse is broken... and the characters remember who they once were. At first, there is a revolt and demand to be returned to their home, but it cannot be done. Many people are determined to leave the town, because crossing the town line means reverting to their Storybrooke-Only memories, but they are convinced to stay and embrace both selves.
Mr. Gold finds a way to cross the border without losing memories...
Foreigners are allowed to enter Storybrooke, though it's rare...
( Storybrooke )
Storybrooke is a little, pretty town where everyone knows your name and, strangely enough, visitors are very rare things, and none of those seem to settle in permanently.
The town is run by Mayor Regina Mills and policed by Sheriff Emma Swan.
There are woods, a mine, and a harbor encompassing Storybrooke.
Everyone that lives within Storybrooke is a character who has come from a fairytale with only two notable exceptions that you don't care about.
Before the curse is broken there is no magic in this world. It is a modern-day Earth.
Shortly after the curse was broken a tiny bit of magic was transferred into the town limits.
( The Enchanted Forest )
Is a world where fairytale characters mesh together in one, big soup. It's a loosely medieval/feudal setting. Magic and monsters exist here.
( But Frankenstein isn't a children's fairytale! )
Right you are!
Victor Frankenstein is, in fact, a foreigner from a land called The World Without Color, aptly named for the fact that everything there is monochromatic.
The only reason we have for his being pulled in by the curse is the fact that the Doctor came to Storybrooke via a magic portal and interacted with the Queen who made the curse.
( So far, we know that Wonderland is a separate world from the Enchanted Forest )
Which means that, technically, no characters from those stories can come to Storybrooke via the curse.
Funny enough, however, we do have a Queen of Hearts and Mad Hatter, but without spoiling the series, these characters have very plausible reasons for being there.
( Other Notable Character Exceptions **SPOILERS** )
Some characters from The Enchanted Forest have not come to Storybrooke. These include:
Mulan
Aurora (Sleeping Beauty)
Lancelot (via Arthur Tales)
World-Hoppers:
The Mad Hatter
Captain Hook