Music
 
“You are a fool, sister. You know you are no match for me.”  
“Of all ponies in Equestria… why you??? You were stronger than this!”  
“I am stronger than you ever imagined! I can feel the universe tremble at my approach! Even the GODS know my name!”  
“Nopony will remember you, traitor! I will see to that!”
 
“Pathetic… You were great once, before doubt addled your will. Before you rendered judgment on the Crystal Empire; before you murdered the innocent and guilty, all in one stroke! You weak, sorry fool!!! How does it feel to have slain millions; TO HAVE BETRAYED YOUR OWN FAMILY???”  
“I betrayed NOPONY! Innocents die so that Equestria may live! I ended their suffering, as I will end yours!”
 
“You have beaten me… I cannot believe it… I was wrong, sister; so wrong… I thought I was strong; strong enough to control it! I wanted to use the power for good; for Equestria! You must see that! You must… give me the chance to make amends! To seek redemption!”  
“If redemption is what you seek… then that is what I will give you…”
 
“This is the fate of traitors! Remember this, and do not stray! If you do, I will be ready to render you the same service…”

This soundtrack should’ve been playing (just the first 80 seconds) as Princess Celestia was gearing up the EoH and banish Nightmare Moon to the Moon, only ending when Twilight comes back to her senses. It better conveys the Celestia’s pain in doing what had to be done.