Nightmare Moon definitely didn’t get enough screen time, not with all the possibility and depth to her character. She was so simply drafted as “the bad pony” thrown in and out, used to add depth to a pony who hardly gets any screen time as it is. Just a character builder instead of the twisted, deprived, insane born creature she was. I would have loved to see some scenes with Nightmare Moon gaining claim to power for a short period, and when she stands before her new subjects expecting praise and loyalty as her sister got, she instead witnesses as the ponies cower in fear from her. And the Luna within watching it, drops further into herself, and her bitter born creation strengthening power in unison.
 
Luna, driven to insanity over jealousy, locks away the part of her that understood right and wrong, replacing it with a being who only knows want and greed. Now her sorrowful cries are silenced within the insanity, and all that echoes from those desperate pleas to be loved, is a cruel twisted laughter enforcing all to praise her - or else.
 
“If they won’t love us, then they’ll fear us.”