@PonyPon  
Why? And even if they do have such a form (they’re sirens in Equestria)…  
They’re not pony-antagonists, they’re still originally sirens.

@Liggliluff  
They might have pony forms.

The Dazzlings aren’t ponies … they’re sirens.

Aria Blaze all the way.

@Zambonifofex  
Looks like I’ll have to interpret the vague answer as “Starlight Glimmer”.

@Background Pony #8480  
Kidnapping a princess is fine if your indoctrination methods are well designed, which they were. Even Twilight admits that she’s not sure if she could take much more, and that was only after two days. Plus, if the overall goal is domination of Equestria, taking care of Twilight would have happened sooner or later, and it’s a lot better to do it when you still have the element of surprise on your side. The reason they took less than a day to catch on is because starlight intentionally revealed it, and despite their suspicions all six were effectively deceived and incapacitated.
 
And it’s flat wrong to say that the townsfolk didn’t follow her. Even the ones that want their cutie marks back still admire her, and the fact that they’re forced to make it a secret demonstrates her grip on the populace. They’re totally with her until they they find out she’s been lying to them.
 
Just because she’s a hypocrite doesn’t mean she doesn’t believe in what she preaches. She felt that it was necessary to make herself an exception to her own rule in order to spread her ideology, but it’s not like she’s really gaining anything from living in the middle of nowhere with a town full of brainwashed ponies with no talents. It isn’t luxurious or comfortable, and a pony with her talents could easily live a life of extravagance and influence in Canterlot or Manehatten. She’s definitely megalomaniacal, but she’s not doing it wholly for self gain either.
 
And yeah, she escaped. It’s not like Twilight stopped following because she was lazy, Starlight Glimmer already managed to incapacitate all of them and nearly killed the other four, so it’d be pretty dumb to run into a dark cave after her, especially considering that she probably knows the caves well and is willing to just straight up ice anybody that gets in her way.
 
Compare what she did with the resources she was given, her special talent and a village full of devotees. Most of the other pony antagonists are pretty laughable compared to her in terms of plotting, guile, manipulation, and willingness to kill.

@Somber Star  
IIRC, it is at least implied, if not outright stated, that Sunset’s goal was to take from Celestia what she felt was rightfully hers. But either way, the rush she got from dominating others and showing off what she was capable of definitely started to go to her head at some point. Which would explain why post-rebirth, Sunset Sunset seemed to regard he old self with shame and sorrow.
 
 
@Somber Star  
Ironically, the only thing I can think of that would have nudged her in that direction would be the very mare who least wanted to see her go down that path: Celestia herself. Twilight’s greatest fear is to let Celestia down, which caused her to devote more and more time to studying until it started getting out of hoof.
 
@WaffleBandito  
The sirens aren’t ponies either.
 
Also, I’d like to amend my previous post: Their songs are absurdly catchy, and they have the slick sort of charm where even if you know they’re con artists, a part of you still wants to fork over cash just because they’re such a class act. They’re nor particularly powerful, nor are they evil masterminds, but I can’t help but think that if their goals were more sinister than simple get-rich-quick schemes, their charm and style and masterful showmanship, coupled with their utter lack of scruples, could make them genuinely dangerous. Not becaue of what they could do, but because of what they could potentially get others to do.
 
 
@drumpowa  
Actually, what I was saying is “imagine how much worse it would be if she hadn’t at least had him around.” At least with him there, she was talking to someone, even if not her actual peers.

@Somber Star  
The way I justify how she was antisocial in spite of a rather well off upbringing it is that Twilight is highly intelligent so her love of learning was all that she needed. Think of her as the one that doesn’t participate in class but gets 100 on all her tests.
 
And as far as @Somber Star I agree that they are foils or shadows but I just don’t think they were just foils/shadows, hence my explanation.
 
@Scrounge  
I think what needs to be pointed out that that, even though Spike helped her out, there was some resistance from Twilight, especially early on. There still might be some slight resistance now, but she has learned or is learning to start trusting him and others.

@Scrounge  
As far as Sunset is concerned, power is not a goal. It’s a tool. Sunset is indicated to be a smart enough pony to not go around trying to collect power without having an initial motivation in the form of what she intended to do with it. Which I’m willing to bet is battle Nightmare Moon upon her return, because since she’s supposed to be as intelligent as Twilight, then it stands to reason that she would have figured out that it would be soon.

@Scrounge  
Possibly, but it’s hard to say. The way Twilight’s backstory has been filled out by canon throughout the course of the series, it’s hard to guess why she’s antisocial at all. Her parents seemed like nice ponies (especially by Canterlot standards), she had a great babysitter she actually remembers and a positive relationship with her brother. Twilight had no reason to develop antisocial tendencies, and her obsession with books was derived from taking joy in learning rather than trying to escape her environment. If anything, in a city as big as Canterlot, she would have found and joined a book club.

@Somber Star  
The best defense of Sunset Shimmer, from where I’m standing, would be “her remorse is genuine and she’s working hard to make amends and fix the damage she did.”
 
Also, there’s an earlier divergent point: Spike. Even when Twilight was refusing to get out and socialize unless a friggin’ royal decree was made (which, as you pointed out, it eventually was), she still had Spike. He probably helped a lot in keeping Twilight from going astray.

@drumpowa  
I appreciate the sentiment of trying to defend Lightning Dust and Sunset Shimmer, but I don’t agree with the perspective you’re presenting.
 
Lightning Dust, Sunset Shimmer, and Suri Polomare are respectively, Rainbow Dash, Twilight Sparkle, and Rarity as they would be without the influence of their friends.
 
Lightning Dust shares Rainbow Dash’s skill, ambition, recklessness, and self-centered nature. What she doesn’t have is anypony to restrain her flaws and promote her assets. Worse is that appearances indicate that had RD not ratted out LD to Spitfire, her antics (which would have gotten her hell in a real military) seemed to have been poised to secure her future in the Wonderbolts.
 
Sunset Shimmer shares Twilight Sparkle’s intelligence, power, studiousness, and devotion to her goal. In fact, the divergent point I see between the two happened in the pilot episode: Princess Celestia ordered Twilight to go to a small, cheery town and make some friends. This is apparently the result of learning from the mistake that converted Sunset into an enemy.
 
Suri Polomare shares (unlike the previous two, to a lesser extent) Rarity’s talent for and interest in fashion and likewise the dream of making it big in that world. Also her tendency to emotionally manipulate anypony who gets close to her in order to further her own ends, something which Rarity briefly learned not to do. As with the previous two, it’s apparent she hasn’t had friends to temper her ambition, and consequently she sees nothing wrong with sacrificing any and all emotional attachments along the way to the top. However, it also means that were she to make it there, her position would be tenuous at best, because everypony she’s ever met would hate her.
 
 
@Background Pony Number 17  
I think it’s more accurate to say it casts her as a great portrayal of moral relativity in action. As you said, she did what she did because she believed deep in her heart that she was bringing friendship and happiness to other ponies, and she attacked Twilight & Co. because she believed they were taking that away. She’s not evil, just wrong in a way that happens to be harmful to those around her. She needed to be stopped, not punished.

@WaffleBandito  
If nothing else, their songs are catchy.

@Nukechaser  
Intelligent? She kidnapped a princess. That was an absolutely terrible long-term plan.
 
Deception? It took less than a day to catch on to her shenanigans.
 
Persuasion? Even her own people didn’t really embrace her mumbo jumbo.
 
Ideology? Yeah, which turned out to be founded on hypocrisy. At least the others where honestly selfish.
 
Got away? They let her go.
 
2/10, fails for everyone.

Starlight, by a long shot. Most intelligent, best at using deception, persuasion and surprise, actually has an ideological reason behind what she does that has concrete roots in reality. Also, she got away without a scratch.

@WaffleBandito  
Ah, you see my point then!  
Another issue: On occasion, one of the main characters or ‘aligned good’ characters is the antagonist, such as Grown/Growing Spike. That was one of my favorites simply because he was a character they wouldn’t (and couldn’t) harm.

@That One Guy  
Oh true. Even though this is only showing “pony” antagonists, why aren’t the Flim Flam Brothers shown? They deserve an honorable mention at least!

@WaffleBandito  
Yes, the latter would be true. Still, that leaves a number of antagonists unmentioned.

Pony Discord. Period.

@Background Pony #7C53  
решено

Да не будет анти-6 в сериале, успокойтесь. Не нужен такой сюжетный ход.

@Evowizard25  
turns out sombra wasn’t a pony to begin with so would not belong on this list (either should the dazzlings)

Sunset Shimmer and Trixie are no longer valid antagonists

Suri Polomare, cus she cute