Talk:Princess Twilight Sparkle - Part 2/Gallery/@comment-8761361-20131214023203/@comment-26973802-20140123180528

Her jealousy had already been magnified to its highest point by King Sombra (in my headcanon, for now) which corrupted her. And once she took that final step to move against Celestia, that's when it manifested into Nightmare Moon. Luna was obviously resentful on her own, but probably wouldn't have gone that far if the "outside force", which I think is King Sombra (given they don't seem able to come up with any new villains for two-parters, they can't use the G1 villain Tirek, Chrysalis couldn't be the one, and Starswirl the Bearded would be corrupted by Nightmare Moon's magic when she was banished), hadn't have magnified her bitterness. Also from the way Luna says she missed Celestia so much, she was probably still concsious deep within Nightmare Moon, without the bitterness as it was in control of her body, kinda like Marik