((Alright, I guess I'll start there then! Thanks, guys!))
Mirror Tree - her hooves slid silently down the long corridor as she listened to the sounds of breathing from the colt at her side. He looked bored, but alert for any sign of trouble. He held his wings close to his body, and looked tense. She did not stop this, as it helped him. Instead, the mare turned her focus to the breathing of the guards. She'd put them to sleep without them laying down, to make it appear as if they were still awake. She'd used words, of course, told shut down every part of their brain but the one that told them to stand, breathe, swallow, and other unconscious functions. Then she and Decode slipped easily in.
The mare sped up her pace and pulled open the door at the end of the hallway - which led directly to the throne room. Decode followed her in.
There was no one inside, which was perfect. But they would be here soon, and she would be there to begin her plan...
Decode - as we entered the throne room, I saw mirror tree come to her decision on character almost instantly. He decided to quietly go along with her, but let her do the talking. These were royalty after all.
But he could definitely see that canterlot castle was not where he would normally find himself. Too roomy.