Somewhere
-One month after Luna's return-
Luna woke up in a room that was dark. It took a moment until she noticed she was chained to a rock.
"Where am I?" she called into the darkness. But nobody answered her, only her own echo came back. When she tried to break free from her chains, she noticed her magic was weak. She still hadn’t recovered from Nightmare Moon, that was why her mane and her tail weren't shining. She squirmed in her chains, which, of course, did not help. Her wings hurt because her restraints tugged to them.
"The chains a breaking my wings" she yelped into the darkness again but just as little as before got an answer. After some time she heard a door open and somepony came into the room. The hoofsteps came closer and closer. As her eyes slowly adjusted to the darkness, she could see who came up to her. It was an old unicorn stallion with a robe, but she couldn’t spot anything further. Tatarus! She could not even see the walls or the ceiling of the room.
"We will cleanse thee, Nightmare Moon" announced the old stallion.
"Thou shalt be purified by this ritual, so that thou can never harm anypony again"
"I'm not Nightmare Moon" Luna objected, again her voice was weak. However, the old stallion ignored her and continued.
"We will lock thee up, lest thou never afflict us with"
"NO" She screamed and wriggled her chains.
"Let us begin!" On the stallion’s mark, ten Pegasi took off and started to fly in a circle.
"Let in the sunlight!" Four Earth Ponies pulled a rope and a stone slab in the ceiling slipped aside. The sun shone straight upon Luna’s face and blinded her. She had to close her eyes as the light brightened the chamber. The old unicorn began to weave a spell and the light continually grew brighter.
"Stone! Stone! Stone! Stone! Stone! Stone! Stone" chanted the Pegasi rhythmically.
Luna screamed as her fur started to burn. Slowly and painfully, the flames were working ahead. Where the fire had raged Luna’s flesh was petrified and cracked. She cried and cried. However, it did not stop and the ponies around them increased the tempo of their chant.
She cried and screamed until she lost consciousness
-At night-
Screams echoed through the room and told of her suffer. Luna suffered agonies which nobody could ever bear. She had been fossilized, though not completely restructured because she was an Alicorn.
Long after all ponies had disappeared, the flames were extinguished.
She continued to cry, it was a cry of hatred, suffering and revenge. Luna felt nothing except that.
"I can help you" whispered a disembodied voice in Lunas ear.
"I can exact revenge for you and punish those who did this to you"
Suffering! I want them to suffer!
"I thought so" purred the voice.
"Set me free and I’ll lend you my hoof for your revenge!"
Tears ran from Lunas eyes as she chose.
"I'm sorry, Tia" she whispered. The once beautiful mare was broken! All she now wanted was her torturers to suffer. So she set her free. She could do what she wanted as long as she made sure that Luna got her revenge.
"I'm so sorry…"