They waited, and waited, and waited, until finally, they saw a figure flew through Ponyville's barrier, no doubt she was able to because of her superior magical talent. She flew straight to the library. Her white coat was singed black and her mane was completely messed up. It had even lost its ethereal luster, and it now appeared as a regular pony's mane.
"Celestia! You-" Applejack started.
"I know, girls. Sorry I took so long, but those shadows attacked Canterlot and I had to do something about it. This barrier is no problem for me and once it is destroyed all of you ponies can flee!" Celestia focused on her spell and shot a beam of bright white light onto the darkness, expelling it entirely.
The four ponies cheered as they watched it crumble and dissolve and reveal an ironically shining sun against a blue sky. Their smiles disappeared as the perfect sky was clouded over with black fog. Thunder clapped and out of nowhere Twilight appeared again.
"And just what do you ponies think you're doing?" Twilight shouted, but then she noticed her old teacher, Celestia. "Oh, Princess" She said, feigning a curtsy, "I hardly recognized you without your white coat and flowing mane. You are weakened with every minute I'm here… You really should've brought Luna with you, she could've withstood my darkness far better."
Celestia grimaced. "I'm still strong enough to defeat you! But this isn't how it has to be-"
"Oh, blah blah, friendship, friendship… Save it, Celestia. I've far surpassed the rank of student, I don't need your silly friendship lessons anymore. I'm going to enjoy this."
Twilight disappeared and reappeared behind Celestia and shot a magic beam at her. Celestia turned around and countered. The two ponies, student and teacher, held their focus for what seemed like forever. But Twilight was right, Celestia's light magic was being weakened by the dark influence Twilight had over the land. With every passing second, Twilight's beam inched closer and closer to Celestia. The Princess put all of the power she had left into one final burst of energy, but Twilight was prepared and shot right back with twice the force. Celestia was pushed back into a tree 50 feet away. Celestia struggled to look up at the ponies one last time. She whispered inaudibly, "I'm sorry… every… pony…" She slumped to the side and was still.
The ponies cowered, but Rainbow Dash quickly discarded her fears and stared at Twilight defiantly. She had had enough of this. She flew to Twilight's level and screamed, "How dare you! That is your Princess, your teacher! She trusted you more than any pony else! Doesn't that mean anything to you?"
"Frankly, no."
"You!-"
"Oh, Rainbow… Always so loyal, but you'll see soon enough, your loyalty will prove to be your very end. But for now," Twilight said as she raised her hoof, "Now, you shall sleep." She waved her hoof over the ponies and a twinkling powder fell over them, causing the ponies to faint one by one. The last thing they head was Twilight's insane laughter.
When the ponies awoke, they found themselves in a dungeon. Applejack checked to see if each of them were alright, and was relieved to find Rarity and Spike were with them, alive.
Applejack saw a familiar white figure lying in the corner. "Celestia! Yer alive!"
"Listen girls, we don't have long. You still have the elements, you must use them!"
"But, Celestia, we don't have our sixth element!" Pinkie Pie said.
"You forget, my little ponies, that I used to wield all the elements myself when I imprisoned Nightmare Moon. I will be your element of magic. Trust me."
"We trust you! Let's do it!" All the ponies agreed.
Twilight walked gracefully down the stairs into the dungeon. "Ah, so you are all awake now. Even Celestia. I really thought you would have been dead now, dear Princess. Hmph. Well, no matter, I shall kill you at dusk… Oh wait, that's all the time! Muahaha! I have created everlasting darkness! Your subjects shall live in fear of my dark night! Ah, Nightmare Moon would proud wouldn't she? And she is… I have seen her. She came to me and told me she had been waiting for this. With her help, I cannot be stopped!" Twilight explained as she inched closer to the ponies.
"You beast!" Celestia spat out.
"Die now, Celestia!" Twilight shouted.
"Now, girls!" Applejack shouted and they drew closer together in formation. Celestia struggled to a standing position. They each channeled as much power as they could and shot a rainbow of light at Twilight. It encompassed her in a thick rainbow wall as Twilight let out a scream. The ponies smiled at each other, brohoofing their victory. And they would have celebrating more, if they had not heard that maniacal laughter once again.
"You imbeciles… Did you honestly think that you could defeat me with rainbows and friendship? Pah! I am far above that nonsensical idea. You have only made me stronger by fueling my hatred. And now I have no need to expend any more energy on killing Celestia, so thank you. Ta-ta!" Then Twilight was gone, leaving the group alone once again.
"Celestia, is it true what she said about Luna?" Fluttershy asked.
"No, Fluttershy. Luna would never betray us, not again. She is noble and loyal. She watches over Canterlot as we speak."
The ponies all looked somewhat relieved.
"Now, girls, I'm afraid I will not be alive for much longer, I can sense it."