Jizz

As Spike became a dog in Equestria Girls, it must be that dragons in general transform into dogs in the human world. Thus, if a full-grown dragon were able to enter the mirror, it would transform into...

mylittlepony

Sunset Shimmer and Spike the dog (audrarius)

ClopClop, FapFap

Dog Spike [MM] (Spotty_The_Cheetah)

BronyvilleRS