Backstory on what happened 1000 years ago in MLP is very poorly expected, sure it say that Nightmare Moon wanted to bring eternal night, and that Celestia banished her.



But just think about motive, Luna turned into Nightmare Moon to stand up again her sister and to be loved and respected, not to blindly kill every pony.



There was nothing mentioned about revenge " I will kill all ponies because they ignore my night ", so I do not buy " Luna go evil and want kill every pony on the planet because she is night, dark evil ", the only reason why we did not got more Luna in the show is because Hasbro decided that she must be evil bad sister and that children's would be afraid to watch her.



From what I saw in first episodes of the show, Nightmare Moon come back after 1000 years of banishment, but I do not see insane monster, I do not see Alicorn mad of revenge for banishing her to prison, she is regal, calm, focused on her goal, she knock out guards what attacked her, but not kill them.



When she discover that mane 6 want to get elements, she could just rush in and kill them, instead she take indirect actions what are meant to scare of mane 6 ( how long it would take Celestia to kill Twilight and her friends, Nightmare Moon did not wanted to kill any pony in the first place.



Also, I do not buy that Celestia got banished, because first off, should not it be long epic battle between sisters where Celestia is banished, instead she just does not show up, Nightmare Moon does not have any damage on her body, and Nightmare Moon arrive not long after the celebration start, not enough time to even face her sister, not to mention, it would be to big event to just happen off screen ( and if Nightmare Moon would beat Celestia so easy, why would she have problem with mane 6 ).



I just do not find Nightmare Moon lethal or evil or stupid, I do not buy that she would not know that food can not grown without sun, she had to have plan how to keep her subjects alive.