Actually, I don't think mocking her was his intent. He was trying to convince others that he really was Fluttershy, so he was trying to act like how he would expect Fluttershy to act. He listed off her interests and her special traits (like talking to animals). Yes, I can understand why he would potentially want to mock poor Fluttershy (especially when she was ignoring him) but I don't think he was doing that at the time. Also, even if he *was* mocking her, he wouldn't say something like that unless there was some validity in it (It was probably something that Fluttershy told herself and Angel, and didn't really want anyone else, including Discord, to know about)