Criterians are very hard to find any mention of. If you look long enough, though, you can find a great deal of information. They are very odd creatures, being humanoid in body shape, and bipedal, but beyond that, they are a mishmash of many things. This is a collection of the various things I know about them.
Criterians are human in basic shape, so imagine a human as a base template. They have horns if they are female, and antlers if they are male. Their hair is mostly normal, but is always naturally neon in color. Their ears are always upward pointing, like a deer's. They can often see in the dark, and because of this, most are biurnal or nocturnal. Their arms are often that of a feline, although dexterity remains in the toes of the paws, the reason for which is unknown. They have normal genitalia, respective of their gender. They can have anywhere from one to five tails, although three is the most common. The tails are usually bladed. About half of the population has wings, and while most are feathered, insect and bat-like wings have been seen. Their legs are normally hooves, they are full hooves if female, and cloven if male. They usually wear clothes the color of their hair. They can live for an abnormal length of time, up to 500 years.
Criterians live mostly in small groups of four at max. They are mostly antisocial. But because of their long life, this hardly matters. The are capable of producing low level illusions to make themselves look human, to a degree. They are usually short tempered, and have little patience. They love getting into fights, and will often make groups dedicated to said fighting. They have a strong this for knowledge, and will often spend hours at libraries reading on all that they can.
When Criterians are disguised as humans, they act almost entirely like humans, but are completely aware of their body parts that are hidden. If, however, they are a changeling, then they will grow up thinking that they are human, and will have a constant disguise running because of this. Eventually they may experience feelings where wings or hooves would be. If this happens, the outcome depends on age. If they are a young child, anything said will not be taken seriously. If they are a teen, then they will most likely keep the feelings to them self. If they are an adult, they will either keep it to themselves, or seek mental 'help'. Of all of these outcomes, the mental help outcome is the worst, while the kid outcome is the best.