Startled by the realization that you can feel the costume’s tail moving as if it were part of your body, you nearly fall over before catching yourself on the metal bar attached to the wall. After the shock wears off, you concentrate on trying to hold the tail still by just thinking about it. Unsurprisingly, it works! Wait, does the tail feel heavier, or are you imagining it? And it’s definitely gotten thicker!
You barely have time to process this before you hear a loud popping noise from your leg joints. You fall to your knees as the bones in your legs reshape themselves into those of a feral deinonychus. Despite the violent restructuring of your skeleton, the process remarkably remains painless. When at last you are able to stand, all trace of the costume ever having a zipper has vanished, and your body has fully adopted the shape of a feral deinonychus. The eyes looking back at you in the mirror are now a bright orange with slit, black pupils. You open your new maw, finding no trace of your human face within what should have been a mask. Attempts to speak result only in a series of inhuman squawks and screeches.
The first thoughts that come to mind are about how awesome this is. You’ve become a living, breathing deinonychus! This is a dream come true! However, as the adrenaline wears off, anxiety begins to set in. What if this is permanent? How can you go back outside like this? You can’t even speak anymore - you’ll only ever be seen as a wild animal, a dangerous carnivore! You begin to imagine all sorts of terrible fates - shot by a scared farmer, hunted down by a frightened mob, captured by the military to be brainwashed into becoming a secret bio weapon, dissected by mad scientists…
Before the panic can really set in though, you notice another strange phenomenon. Glancing around the fitting room, you swear the walls are starting to become somewhat transparent, and there appears to be a faint image of some kind of stable stall transposed overtop the fading room. You blink twice and shake your head to make sure you aren’t hallucinating, but instead the image of the stall becomes clearer while the fitting room fades even further. At last, it all clicks into place: you are phasing into a different reality!
As the last vestiges of the costume shop fitting room fade into nothingness and the wooden stall solidifies into corporeality, you feel a sudden addition of weight on your head and body. Turning your head to try and look at your back, you catch a glimpse of spiky, black metal plates edged with gold covering your hips and tail. The creaking of metal as you turn your neck informs you that similar armor now adorns your neck and head. It wouldn’t be much of a stretch to assume some sort of saddle now sits on your back, you figure.
It seems your present fate is the life of an exotic mount. Nothing much to do in this stall but lie down and wait for someone to enter.