Sort of an expansion on the ideas I was working out with my mahou shoujo take on Equestria Girls, set after the movie. My explanation for Spike being a talking dog when he comes through the mirror is that his EG counterpart is also a magical creature, but of a different sort: he’s a weredog. His full human form is actually quite large and powerful, though his senses, while sharper than a human’s, are nowhere near as sharp as his full dog form. He also has a hybrid form which blends the power of his human form with the sharp senses of his dog form. In a bit of a turn-around, Spike in this universe acts a bit aloof toward Rarity due to his conflicted feelings of attraction toward her and loyalty toward his “sister,” one of the villains. Rarity, meanwhile, has developed a very obvious crush on him, despite him being a sophomore while she’s a senior (he looks older due to his size and the goatee).