@Dirty Bit  
I literally mentioned this in the comments below, you can see for your self and all the responses I got was that they are hipocampuses.

@steve the hammerhead
 
Same :U

@Dirty Bit  
Knew it.

@AntarcticRainbow
 
They’re confirmed to be sirens :3

But can you imagine the sea ponies being sirens?  
That would be next level shit.

@Justice4243  

@Lawful Girly  

@Dirty Bit  
Hey, just gonna leave this here…

@Justice4243  
Or the writers will have forgotten about them.

@Dirty Bit  
I would! X3 And I am, but I don’t usually write, so here goes!

@Justice4243
 
Awwwww…Sonata :c

@Lawful Girly
 
If you’re on FIMFiction, would you give me a holler? :3

@HighRollerHydra
 
Spoiled since it is a rather major movie spoiler  
||  
‘fraid not. It doesn’t look like they’re remorseful for what they’ve done. They’re basically forgotten as soon the they’re defeated. Sonata was very excited about lunch at one point, so it seems plausible they can sustain themselves on regular food.
 
No idea how not having their gems to suck in energy will affect them.
 
Either way, considering all signs point to their being more Equestria Girls in some form or another, we’ll probably see more of them.||

@PonyPon  
Until at least, they learn how. But I doubt they’d have that manipulative power anymore.

@HighRollerHydra  
Working on a fanfic right now. Working title “Harmless”.

@HighRollerHydra  
Apparently, they can no longer sing(at all) and everyone laughed at them.

@Justice4243  
So nothing was shown on the Dazzlings’ fate after their defeat?

@HighRollerHydra
 
Possibly. Basically Twilight breaks out a book talking about the sirens (yes, the movie confirms they are sirens, at least the Equestrian version). We find out they got really powerful and that Starswirl banished them to a world where he didn’t think they’d be a threat. And that’s all.
 
So there’s no telling if Starswirl was being merciful, if he thought this other world was a fate worse than death (the Dazzlings were certainly unhappy), or if he maybe had a limited amount of time given the Dazzlings where presumably at full strength and causing a mess of things.

@Lawful Girly  
Never doubt the inherent maliciousness of an old wizard.

@Justice4243  
Wouldn’t “banish” mean to kick out, and not give a sh*t about what happens to them in the new world?

@PonyPon  
Also I doubt he was that cruel.

@PonyPon  
Then again, it’s to promote those stupid dolls.

@HighRollerHydra
 
We’re not really told in great detail why Starswirl picked the EqG world other than he thought they wouldn’t pose a threat there.
 
Who knows if he actually had multiple worlds to pick from.

@HighRollerHydra  
Maybe he thought it was close enough to that.

@Justice4243  
Why doesn’t he just dump them into a dimension filled with killers? Why a dimension with high school stuff?