Well, she's technically the only one royalty in Equestria that hasn't been in some way villainous (I'm counting Cadence because, although she herself isn't evil, Chrysalis is while she's taken her form). So the question on my mind is: Will they have Celestia as a villain in the future? Considering this scene (Sorry about it being so small, I couldn't upload the full size version, too many kb): Spoiler: Season 3 Scene I think yes (She can clearly use some kind of dark magic, which makes her look pretty damn evil when she's using it). What's your opinion?
Celestia? as a villain?! hmm that would kinda sorta work out. I don't know if her multi-colored hair would fit the villain look.
The villain's probably going to use her for these two episodes at the start alone, or maybe even the rest of the series, who knows, but I doubt they'd beat a dead horse *badum tss* by using the same concept twice, I mean even with the return of a *coughs* FAN FAVOURITE VILLAIN FROM SEASON 2 *coughs* they're going to mix that up a little, I don't see how they could do that very well with the simple idea of evil Celestia. Maybe she's got another persona like Luna had Nightmare Moon, Burning Sun maybe? Also Celestia, goddamit why you so bad at fighting villains? Captured by Luna, does nothing to help against Discord, out powered by Chrysalis, and possessed by a Spanish bad Pony Creator OC design. You had one job!
In the new preview for the first episode her eyes did glow green and she did summon up evil crystals... and you have to wonder how she'd react to Twilight proving that the sun would come up without her [video=youtube;bZQ246KDvd8]http://www.youtube.com/watch?v=bZQ246KDvd8[/video]
I think Celestia is one of those characters constantly doing whats best for Equestria, I do think at some point in the series its possible Twilight will learn more about her mentor and/or that something she does will be seen by Twy and the others as villainous, but I don't think she will actually ever become evil herself. I mean its obvious Celestia has her fair share of secrets, the talk between her & Luna in the season 3 preview is proof enough of that I mean a test, getting Twilight ready for the next stage of her Training. As much as I hate to say it, seems like Twilgiht is just a Pawn in some sort of grand game Celestia is playing, that in and of itself is kind of villainous, even if it is for the good of all. *Personally I imagine its probably something like getting Twilight Ready to someday take her place someday or some such, but still, you never know could pull a 180 and end up something else* But yeah, I think the only time we would see an Evil Celestia would be if Discord got to her and used his powers to Inverse her, because as far as we can tell He's even more powerful then Celestia *being able to manipulate reality and what not*
If only she will be zombified or possessed. Because, you know, she is kinda Gandalf/Yoda of the show.
Seeing Celestia as a villain would make a very interesting episode. If it were to ever happen (Which I honestly doubt), it would most likely be a two part episode. Given Celestia's amount of power which we've already seen, I feel as though an episode like this would require an epic fight between her and Luna (See Pokemon: Mewtwo Strikes Back, then think about that idea.) That would be pretty cool. I can't elaborate any further. Doing so would cause me to collapse on the floor because of a lack of this episode's existence.
I have seen so many MLP parodies of Celestia being evil or doing evil things, so I wouldn't be surprise if she turns up evil.