@Frustration in Excelsis  
I think the vampire thing has some merit to it. I was even talking to someone else about Bat Ponies and they had a headcanon of them sucking blood (a headcanon that I honestly don’t care for them).
 
I agree. It’s probably for the best that they don’t get that much spotlight.

@mjangelvortex
 
Aaah. So much for my hypothesis, then.
 
Perhaps it was the association between bats and vampires? Perhaps something else. Regardless, the fanon bat ponies don’t have much in common with what little of canon bat ponies we’ve seen on-screen – I would argue that they’re by and large the most internally consistent original species in the fandom. Which is not a bad thing, I should point out – if people like a concept they’ve collectively come up with, more power to them – but still worth thinking about.
 
Honestly, the degree to which fanon bat ponies have diverged from, well, this clip here is part of the reason I’m kind of glad the show hasn’t brought them back. The other is how popular they’ve become in the fandom – whatever the show might do with them, I really do not think it’s going to be possible for it to live up to five years and change of hype, and any intepretation the show takes is going by necessity to invalidate any other take on them. Better to leave them as an open concept for fans to do with as they will, I think.

@Frustration in Excelsis  
Exactly that. The fangs weren’t but there was fanart of Bat Ponies that came out before Flutterbat that depicted them with fangs. Regardless of that episode with Flutterbat or not, that trend pretty much stuck.

@mjangelvortex
 
Personally, I figure that the fangs thing might have started out from some confusion arising between Luna’s chariot pullers and Flutterbat. Both are bat ponies, after a fashion, and the guards here got a few seconds of screentime tops while Flutterbat got a lot of screentime and focus. Flutterbat’s fangs were very prominently displayed, and unless you’re particularly pedantic about going back and looking over screencaps of brief moments like this (like, ah, like I am), it’d be easy to not notice that these guys have regular teeth, especially since the motion throughout this clip makes getting a good look diffcult. Factor in some years of everyone giving bat ponies fangs, and you get where we are now.
 
So what might have happened was that the fandom’s perception of bat ponies was nominally based off the very brief clip that started the idea, but in practice was influenced just as heavily, if not more so, by a later canon concept that was similar in some regards but was a distinct thing from the one that started the whole phenomenon. Fanmade bat ponies also have regular manes, unlike these guys.
 
Unless bat ponies were depicted with fangs before “Bats!” came out, I suppose. I don’t know if they were.
 
I suppose this was a bit like the development of the more popular background ponies or headcanons. You see something repeated often enough in fanfics and forums and it’s easy to forget it was not depicted so in canon, especially if the thing being talked about only appeared very briefly or was never discussed at all.

The fangs were a fanmade thing.
 
@neo4812  
That’s a possibility too but Bat Ponies were originally intended to be an actual race in series.

G4 is soon over. Still not too late to bring batponys in. Sigh… . Stabs Hasbro!

maybe its like a costume, cause dash had batwings in the cutie re-mark so its profanely like something that she makes them wear