I doubt that whatever corrupted Luna is more powerful than Discord. Discord's a
god after all. If anything, it would be more cunning or cruel, but not likely more powerful. Discord pulls the strings, not the other way around.
Here's what I think:
Luna's anger/jealousy/[insert negative emotion] woke...we'll call it "Nemesis" for lack of a better name. Nemesis found Luna and said, "Hey, I know of a way that you can become powerful enough to overthrow your sister and take the world for your very own, " because that's what villains do. Luna said, "Okay" because that's what sad, jealous anti-villains do. BAM! Night Mare Moon. BAM! Night Mare Moon is banished to the moon by an Elements-wielding Celestia. "All the better, " Nemesis thought. "Let her sit on the moon and get
really good and angry." After 1000 years, Nemesis sent a few stars to destroy the seal, knowing that enough time had passed that Celestia would be "out of touch" with the Elements of Harmony. How anypony knew this would happen (the prophesy) is anypony's guess. Night Mare Moon came back, and in a surprising turnaround, 6 ordinary ponies stripped Night Mare Moon of her power using the Elements of Harmony. Luna was completely aware of what she had done during her time as Night Mare Moon, but couldn't stop herself. Nemesis' power was too strong. Hence why she apologized when she was finally returned to normal.
Nemesis sat back and watch as the sisters' former foe, Discord was broken out of his seal, but did nothing more. Equestria was already doomed, as far as he knew. But what's this? This
filly and her
friends used the power of the Elements of Harmony to re-seal Discord. Weren't these the same ones who also defeated his precious Night Mare Moon?
Also, the
purple one. She commands great magics. Not only that, she posesses insecurities that rivaled Luna herself. She could be useful.
Or, you know...what Ace of Scarabs said.
edited 2nd Feb '12 10:34:22 AM by KarlKadaver
Give the world the best you have and you will get kicked in the teeth. Give the world the best you have anyway.