@rautamiekka
For me it’s a weird scale. It’s like with monster girls or monster boys: they gotta have monster parts and girl parts meshed together in a way where one doesn’t overshadow the other to count. So like a werewolf is a monster, and a boy or girl, but is so overwhelmingly monster that there’s no boy or girl so it’s not a monster girl or monster boy. Changelings are too overwhelmingly bug to be considered a monster pony for me, but Sphinxy has a clearly defined pony face and build so she is. The face is more or less the set-in-stone criteria for me: a sphinx with a cat face or a cat nose is just a monster or a furry, a sphinx with a human face is a monster girl :P