Fallen Angel

Nightmare Moon had the mane 6 cornered.
"Looks like the elements of harmony are useless after all." She laughed evilly. Twilight stared at the six elements in shock.
"I don't understand. Why didn't they work?" Nightmare smiled manically and charged magic into her horn.

"Time to die!" She yelled and launched a powerful blast of magic at the six of them. They all shut their eyes in fear waiting for the pain to come, but it never came. Twilight opened her eyes in time to see the blast get launched away. Nightmare stared at a figure in between her and the others. The smoke faded and revealed a jet black pegasus with a spiky jet black mane and tail. His eyes were black, and he had two blood red scars on his right eye. The first ran down the middle of it and stopped at his cheek, the other ran horizontally right under his eye.

"Oh my goddess." Rainbow silently exclaimed. Nightmare glared at the new pegasus.
"Who dares defy me!?" she yelled. He ignored her and turned to the others.
"I'll hold her off for now, but you need to figure out how to use the elements." He paused for second and looked Rainbow right in the eyes, something no one seemed to notice (not even twilight, and she's usually the observant one).
"I'll keep you safe, I promise" he looked back the others then.
"I'd prefer to not kill her, but I will if I have too."

Nightmare started laughing.
"You, kill me?" he glared at her. Nightmare continued
"I bet you can't even touch m-" before she could finish he was under her in a second balancing on his front hooves. Before she could react he kicked his back legs out and sent her crashing through the wall. The others gasped behind him in shock.

"Don't worry about this fight, just hurry and use the elements. By the way, the name's Gohan." Gohan turned to see Nightmare getting up rage clear on her face.
"How the hell did you do that!? How dare you strike out at royalty!?" Gohan suddenly appeared in front of her glaring at her.
"Shut it." He said coldly and punched her in the jaw. The sound of shattering bone echoed through the abandoned castle joined by a pained scream from nightmare.

"Gohan, we figured it out!" Twilight yelled out excitedly. He turned to her to see them all wearing strange necklaces, except for Twilight who was wearing a crown.
"Well what are you waiting for? Get to it." He flew behind them to get out of the way. The girls were floating in the charging the elements. Gohan flew up behind Rainbow dash and put a hoof on her back in between her wings and concentrated. After a few seconds a dark black ran next to Rainbow's red beam in the rainbow beam that was headed straight for Nightmare. The beam surrounded her in a massive whirlwind and raised her into the air. When it finally dissipated it revealed Princess Luna a little younger looking than she was just before she turned into Nightmare Moon.

Gohan and the others walked out of the castle with Luna, just as Celestia was landing with a few carriages. She walked towards them and stopped right in front of Luna.
"Hello, sister." Celestia said smiling at her.
"Sister!?" Twilight, Rainbow, and Applejack all yelled out, Pinkie, Flutter, and Rarity were all too shocked to speak. Celestia walked up to Twilight and the rest of the element bearers.
"I'm very proud of you little ponies." Twilight looked at the princess and gave her a small smile

"Thanks Princess but, we would be dead right now if it weren't for Gohan over there." She stated while pointing a hoof at Gohan who was currently standing a few feet to the right. At hearing his name Gohan turned towards them and took a shaky step forward, no longer able to hide how exhausted he really was. Gohan's wings extended for a second revealing a wide gash that was hidden behind his left wing. Gohan was about to say something when he coughed up some blood and fainted from blood loss.