II dont really like trying to get logical about children films, yet at the risk of bordering on fanficky:...
So twilight is suppose to be getting some crown (according to one source), this could either be taken literally, meaning it was why she crossed the portal in the first place, which then leads me to believe the crown is property of Equestria. Or it kight just have meant that twilight is, for whatever reason, attempting to win the school formal and receive THAT crown, which may or may not be the same as said former crown.
I reckon (admittedly based on practically jack squat), that the crown is the main source of the portal, and being that it is of some godly equestrian property; it created a dimension based on Equestria. It was either stolen (by the main antagonist, who wanted to reign over their own created world) or fell in or wtv. Twilight needs to win it back legitimately for wtv reason. Some revelationnwill occur at the end where if the crown returns to Equestria than this new dimension will cease to exist so twilight is like "aww shucks you guys keep it" and then is all like "gee celestia is gonna hate me for purposely failing my mission" and then just like with 50% of the plot of season 3 (example, Spitfire to RD), celestia is like "Awww you're such a swell pony ok you can still be alicorn" credits. "our friendship transcends dimensions we are hip". Then there is a post credits segment where an egil human is all like "muhahaw friendship is magic huh? Well magic dont exist here so..." dun dun dunnnn
Yeh i bsed the latter part.
hope their names dont become too wild...or less wild i guess.