in world of My Little Pony there are a race of Changelings who can mimic anyone they want, In this universe everyone is humanoid so hands and feet other then dragons or griffin's as they have hands and paws for feet

your a student of (Either Luna or Celestia or Candance) as your in the royal castle of who student you are, as slowly through the year you noticed more Changling activity as was slow at first...

Till one day you enter the Throne room to see not one but 2 of the princesses but one is a Changling while one is real. Standing there you can't tell who is the real one and who is fake by appearance or voice as they both are identical in that way

standing couple meters infront of you is the princess (your choice who) and her Changling duplicate both are standing in a fighting stance even though there not fighting yet, before they turn to you giving you a look of 'Who is the real one'