It is true that we don’t know how this is going to go. For one thing the Storm King’s motivations and goals are hinted to be rather shallow (he’s basically a pirate with delusions of grandeur), and though he’s extremely powerful he’s already been manipulated and betrayed by one second in command.
 
Tempest on the other hand is being displayed to be particularly important, has rather ambiguous goals, and has been directly stated to have a dark past.
 
We’ll know more when her comic comes out of course, but for the time being I wouldn’t place bets on exactly who’s going to play what role.

@Background Pony #C99E 
Yea she’s second in command but I wouldn’t compare her to Darth Vader. With her personality so far the relationship reminds me more of Shego and Dr.Draken.

@Background Pony #C99E 
Thing about dragons is they can easily outshine the big bad sometimes.
 
And if the first thing I’d ever seen of the movie was this trailer? 
I’d presume Tempest is big bad and Storm King is a ‘wacky adviser’, considering his only scene they show.

SHE’S- …Okay, she is /an antagonist/, but, she isn’t the Big Bad, She’s the Dragon. Basically, the Vader to Storm King’s Palpatine.

@Background Pony #67B3 
Chrysalis have atleast some kind of originality to it, sombra yeah he is kind of edgy but that level like here :)

@Perteks 
If a dark color scheme and some physical difformities suffice to make a character “edgy”, then by the same account, Queen Chrysalis and King Sombra are edgy too.

Same here, OP.
 
When I heard Emily Blunt was gonna be in this movie, I got 100x more excited.

@Background Pony #67B3 
You like bad design I think its something wrong with you

@Perteks 

most edgy character in all series of mlp