Spike is a chubby pseudo-tyrannosaurid with a dorsal ridge of keratinous spines comparable to an iguana’s. He is extremely stunted for his age, being basically the same size he was as an infant, because his pony caretakers aren’t… really feeding him a proper diet… ideally Spike would eat mostly meat, but the only animal products he has access to in pony society are eggs and diary. He also gets fed way too many “gems,” the magic-dense semiorganic structures that grow like plentiful tubers in the charged soil of Equestria’s magic climate bubble. Dragons flock to Equestria to forage for these rare dietary supplements, but they’re no replacement for the proper nutrition meat would provide Spike. It’s a classic tale of exotic pet ownership, except the pet is like, also a sapient lizard child