Night of the Living Ponies

It was a bright and sunny morning in Ponyville, as I, Twilight Sparkle, and my assistant, Spike, were out practicing new spells. Then, as usual, Pinkie Pie crashed into me as I was casting the spell and ended up almost burning down town hall. She was off to see what Rainbow Dash was doing. She was probably just sleeping on a cloud, as usual, but being how she is, Pinkie was looking for as much fun as possible. After I got up and tried the spell again, the princess arrived. She informed me that her sister, Princess Luna has been acting unusually strange lately. "I'm not sure, but it could be possible that she is becoming corrupted once again.",She told me. I responded as respectfully as I could with,"Forgive me your highness, but I don't think that's possible. Is it?". She went on to tell me how she had spoken with Zecora before she had come to me and how she said it was possible if around dark energies for an extended period of time. I then asked the princess,"How is that possible? We've reformed Discord,banished Chrysalis back to wherever she came from, and destroyed Sombra. There's no dark energy left around.". She then told me that, deep beneath the crystal empire, far beyond the reaches of even her, lies a crystal of pure dark energy, put there by Sombra as a last resort, should he be killed. I asked her how it went unnoticed for so long as well as why Luna is the only one being affected by its power. "Of that, I am not certain, however I am certain that if we let her absorb enough of its power, Nightmare Moon will rise again.",The princess responded. The instant she said Nightmare Moon, horrible memories flashed through my mind of what happened the last time we faced her. At the same time, we said,"We must NOT let that happen!"