Doctor Who stared at her with befuddlement before saying, "Right." He ignored her, turning away, and looking seriously at the pony. "Winter Breeze, aye, my fellow? Captain of the Princess of the Night's royal guards?" He looked angrily at him before realizing that he might not know how his lie had contradicted everything the parchments from the princess had said. He was definitely a changeling. "How...interesting," he said, whipping out his sonic screwdriver, pointing it straight at the pony, hoping to undo it's transformation to it's normal form. Strangely, it didn't work. He calmly smiled and patted it on the top, before pointing it at the pony once more. As a test to make sure it was working, he fired it at the top of the fountain, where water immediately stopped working for a few seconds before spurting water once more. He tried it once more on the pony.
"Alright, now I know you're lying, but luckily you're not a changeling, so let's get down to the truth. Clearly you're not a guard, as you are, well, here. All the guards, as the three of us know from this letter," he said, assuming the pony might not have a letter, "are locked up in the dungeons with the princess. Who are you?" He expertly flipped his sonic screwdriver, placed it in his jacket pocket, and expectantly looked at the pony, who still hasn't told them his real name.
((OOC: This won't have any effects on Hypno, The Doctor just doesn't know that his Sonic Screwdriver can't undo the transformation of the changelings, as his SS doesn't work on living beings. He just thinks that there is a device involved. Of course, none of the other ponies know this either ))