Am I the only one that thinks it's weird that everyone's been doing nightmare night for years but didn't know who nightmare moon was when she showed up in ep one? The only 2 options is either a) it's bee several years since the first ep and they've been doing nightmare night once a year ever since or b) they were doing nightmare night before nightmare moon's return. I never got the impression that twi has been in ponyville for more than a year. It just seems like some odd inconsistency to me, unless this is everyone's first nightmare night.
Whatever *shrugs*
I'll give my opinion on the episode later.
That's a pretty good observation there Zakat.
I guess I was to wowed over Princess Luna and seeing all the ponies in costumes to think of that.
Here's a few things I have to say regarding this.
a.) I doubt it, but it could be possible that a couple years have passed since Nightmare Moon was defeated. It's hard to say when episodes don't follow a story arc and can go in different order than the episode order. Like that balloon graph (or whatever it's called) that I believe Philomena Lord posted here from EqD a long while ago which showed the supposed order of the episodes in a timeline.
b.) It could be possible that they've been doing this for many years and with nobody knowing who she is, maybe most of them, but not all (like Pinkie), did know who Nightmare Moon was, but were too frightened to speak up.
c.) Otherwise this whole thing can just be considered as an odd inconsistency, like you mentioned, that the creators didn't plan on.
Which one anybody believes from these 3 options is up to them.
Unless there's some answer regarding this from Faust or somebody who works on the show, I don't think we'll ever know for sure.