@Background Pony Number 17  
Celestia as the Good Witch of the South.
 
When they did the film version, she played both good witches as the same character. Celestia’s apparent decision to send Rainbow Dash on a dangerous quest across the land when she knew that the Ruby Horseshoes could have sent her home right from the start is regarded as ‘trollish, but entirely in character’ by many.

@Background Pony Number 17  
nightmare moon as the wicked witch of the west, and twilight as the wicked witch of the east you say? since they’re sisters and cadence is luna’s niece that would mean shining armor married his niece… unless cadence is shining’s daughter, then things jsut start to get weird.

Let’s see…starring:
 
Rainbow Dash as Dorothy  
Winona as Toto  
Twilight Sparkle as the (not just merely dead, but really most sincerely dead) Wicked Witch of the East  
Rarity as Glinda the Good Witch of the North  
Nightmare Moon as the Wicked Witch of the West  
Applejack as The Scarecrow  
Pinkie Pie as The Tin Man  
Fluttershy as The Cowardly Lion  
The Great and Powerful Trixie as the Great and Powerful Oz  
Gilda as the Chief of the Flying Monkeys  
and guest-starring the Crystal Empire as the Emerald City.

And I’m sure it’s totally 100% historically accurate.
 
Especially the part about how Rainbow Dash punched Nightmare Moon in the face so hard it broke her armor.