After leaving the castle and getting on a train to Canterlot, Discord and the Mane 6 start talking about Bill.
"I have so many questions about Bill." Twilight starts.
"I'm sure you do," Discord replies," and while I would love to answer them, I've already told you what I know about Bill. Well aside from one thing. While he may not be able to enter our world, he can still project himself into our minds through the Mindscape. That's how he was able to get into your dreams. He may also enter your thoughts while your awake and try to trick you as well, but no matter how good his deals may seem, he always twists them in his favor."
"Ok." Twilight said as the train started to slow down. "We're getting close, everypony."
"The train has arrived in Canterlot." The conductor said over the intercom. Everypony got off the train and Discord and the Mane 6 rushed to Canterlot castle. They were able to pass the front gates easily because of Twilight's royalty and ran to the Throne Room, where Celestia and Luna were sitting on their thrones talking to the high class citizens of Canterlot.
"We're so sorry to interrupt, but we have an emergency!" Discord said.
"How big of an emergency to interrupt a very important meeting?" Celestia asked, clearly at least a bit angered at Discord and the Mane 6's surprise visit.
"A code yellow." Discord answered. Luna gasped.
"Sorry, sister. I must talk with Discord in private." Luna exclaimed. "Come along now." She continued as she rushed out of the room. Discord and the Mane 6 followed her.
"Where are we going?" Twilight asked.
"Somewhere in the castle that is so secret, even my sister doesn't know about it." Luna replied, as she stopped faced what seemed to be a random wall, and fire a burst of magic at said wall. All of a sudden, it began to wobble, kind of like water. "Follow me." Luna then jumped in. Discord and the Mane 6 followed her and went through the wall and landed on a lift. Luna then pressed a button and the lift started to go down. When it stopped, Luna open a door that was in front of them and went in. The room they entered was filled with different magic items and books, including the inter dimensional Spell book that Bill needed. Luna pulled a certain spell book titled "Mind Spells" from one of the shelves and started flipping through it. She stopped. "Aha," she began. "Here it is. the mind protection spell. This'll protect you from Bill's control."
"Wait, why didn't we just teleport down here?" Twilight asked.
"I used this room so I could've helped Bill enter our world before you 6 turned me to stone." Discord began. "So, I had to magic-proof the room so nopony else would find it. Of course, after switching sides, I didn't need it for that reason, so I decided to just use it as a bunker of sorts, but then Luna saw me jump through the wall and followed me. I've told her about Bill soon after becoming friends with you just in case and she was able to find a spell. So, who wants to go first?"
"I'll do it." Twilight answered. She stepped forward and Luna charged a spell and fired it directly at Twilight's horn. After it connected, the blue magic traveled down Twi's horn and she fell to the floor.
"TWILIGHT!" They all scream, worried.
"I'm fine." Twilight said weakly. She tried to get up but feel back to the ground. "Ok. Maybe not. That really hurt. It was like a giant bird rammed into my brain at mach 36."
"I'm so sorry." Luna said. "I didn't how much a mind spell would hurt a pony less powerful then me or Celestia. We normally just get a mild headache and nothing else. However, your still an alicorn. If the spell can hurt you that badly, then it'd likely be fatal to anypony else."
"Then what are we supposed to do?" Twilight asked.
"I think I have an idea." Discord answered. "We may not be able to Bill proof our minds, but we may be able to Bill proof Ponyville and Canterlot." He snapped his fingers and two maps appeared, one of Ponyville and one of Canterlot. "If we put moon rocks here, here, and here," he said as he pointed to three points on each map, putting a circle around each point, "sprinkle some mercury, let's see. I always forget the last ingredient." He grabbed another book from a shelf titled "Advanced Shield Spells" and flips through it. "Oh. Unicorn hair. That should be pretty easy to get." He said as he looked at Rarity. "Sorry in advance, Rarity, but this is for the greater good."
"Fine. Just get it over with quickly." Rarity said. With that, Discord summoned a pair of scissors and cut Rarity's mane.
"What about the moon stones and the mercury?" Twilight asked. "Nopony's even been on the moon aside from Luna when she was taken over by Nightmare Moon and I haven't even heard of mercury."
"Well, even if I wasn't myself," Luna began, "I was able to grab some stuff on the Moon."
"And I've got the mercury covered." Discord said. "As for creating the shield, that's probably going to be more difficult with out other ponies noticing. I was thinking that we should do it at night since almost everypony would be asleep at that time. Since Luna has dream duty, I'll set up the barrier around Canterl-"
Before he could finish, Luna cut him off. "Sorry, Discord, but I'm going to need your help in the Dreamscape. Since Bill is on the loose, I'm going to need somepony else to help me cover more dreams at once in case he enters a pony's dream."
"But what about the barriers?" Discord asked.
"We'll cover it." Twilight answered. "Just give us the maps and we'll take care of Canterlot tonight and we'll handle Ponyville tomorrow night."
"Alright then." Discord replied. "It's not like I have a better idea."
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Then, the field of view zooms out of the dimension and into the Nightmare Realm with Bill looking over everypony in the bunker.
"So they're giving me a day to pull off my plan. Thankfully for me, that's all I need." He said.