You could have used more techniques. Like cross hatching on the stamps. Or maybe possibly threw in a fade or two, or maybe even three or four. You could have added shadows to Derpy and to the letters. As in shadows on the ground. You could have added the Sun, to show where the light was coming from and what the light source was. Without a light source, you will be just confused on where the light was and what the light is. You also could have added another pony, or maybe Spike, so then we could see who Derpy was talking to. Other than that, it's lovely, perfect, epic, etc.