@Background Pony  
I already guessed that EQG would affect FiM in some way. Hopefully all it does is introduce new characters like Sunset Shimmer and make her a new supporting character, the 7th ( 8th if you include Spike ) mane cast member or a villain for Se4 ( unless she decides to say in the human world, is unable to return to Equestria for some reason or ends up being trapped in-between dimensions ).
 
I just hope EQG does not pull a 86’ Transformers movie on us and replace one or more members of the mane cast with new ones. ( Ex. Twilight decides to stay in the human world and/or the rest of the mane cast go threw and up staying there ).
 
Also hope that ponyverse “Brad” turns out to be the thief so when Twilight returns ( if she returns ) we will know that she probably won’t end up with the pony version of him, and depending on what kind of rules the mirror has ( Ex. if you go threw your counterpart from the other side ends up in your world ) she won’t end with the human version of him either.

Sunset Shimmer is so totally going to be in season 4 that it’s not even funny.
 
All those people interpreting Meghan’s tweets about season 4 being “all pony” as meaning that EQG won’t affect FiM are deluding themselves.

@sixtyfour215  
Well, Trixie, Flim, and Flam are all in there already if they count as ‘villains.’

@gg666  

the box ghost!!

@Itsthinking  
It’s the Guardian of course.

@Itsthinking  
You say that, but if she uses the Element of Magic to conquer the human world, she can come back to Equestria with an army of tanks and jets and missiles and holy crap the movie is gonna be disappointing compared to the epic pony war I’m imagining right now.

It looks like it has a mustache.

Say, has there been other villians available to live in Ponyville in this game before?

“I left you through a magic mirror and pose no actual threat to your dimension at all!”

Well, that could be anybody.