Talk:Do Princesses Dream of Magic Sheep?/@comment-4604642-20150712102745/@comment-26973802-20150713030750

Well when the Nightmare possessed her she physically transformed into Nightmare Moon.

Also, Nightmare Rarity directly spoke to Rarity, as well as speaking of her as a completely different pony

It was established in the pilot episode that Luna's bitterness transformed her into Nightmare Moon, but someone hinted that an outside force had a hand in that (could be she was unaware of it). It clearly wasn't the Tantabus or Tirek, so my headcanon is that before King Sombra was banished, he cast a curse to gradually magnify Luna's jealousy until it corrupted her completely. She was still conscious of everything she did just as Sunset Shimmer was when she was a creature demon (and I'm never gonna let that go), and her resentment was still there to begin with

Or they could've just changed their minds about that