That first one would be interesting; it reminds me of the classic fic "Why Am I Pinkie Pie?!?" in which the main character has to convince the rest of the Mane Six that he is not their beloved friend Pinkie Pie, but instead is someone trapped inside Pinkie's head. (Of course, this coming from Pinkie Pie wouldn't actually be too far fetched - so it makes the task that much harder.)

Play around with it and see what you get!