Talk:Episodes, films, and shorts/@comment-26208943-20150203235101/@comment-26973802-20150205174930

If there was a Nightmare Force it has to have worked differently from the comics as shown in Princess Twilight Sparkle, since Luna's jealousy definitely played a role in it and she transformed only when she decided to overthrow Celestia. I don't think it was only her jealousy though, because one of the creators said an outside force was involved.

In my headcanon, that "outside force" was King Sombra. When Celestia and Luna fought him, he could sense Luna's resentment towards her older sister, which wasn't strong enough to make her do anything drastic, so he cast a curse to gradually magnify it, before Celestia and Luna banished him (his curses are established to survive his banishment, after all). Once her jealousy got strong enough, she decided to move against Celestia, which was the final step enabling it to manifest into Nightmare Moon.

Of course because the transformation looked a lot like a Rainbow of Darkness transformation, as soon as I found out the Twilight's Kingdom villain was Tirek I suspected it was him, but he doesn't use Rainbow of Darkness like his G1 counterpart. King Sombra on the other hoof is mysterious, we don't know the full extent of his powers or his backstory but we do know he possesses dark magic that exceeds the power of Twilight Sparkle so until the show says otherwise I will stand by that headcanon.

Interesting theory for the Luna/Apple Bloom episode. Come to think of it, when Luna appeared in Sweetie Belle's dreams it was about her resentment for Rarity, and when she appeared in Scootaloo's dreams it was, though not in the same way, related to her sister figure, Rainbow Dash. So maybe Applejack will be involved in the Apple Bloom episode somehow...