The Unicorns were gentle, shy and peace loving creatures but as you can see in this picture they can look quite fierce when trying to defend themselves.
The only difference between unicorns and horses is this magical horn or “corn” hence unicorn means a single horn. In perpetua they keep their horns invisible most of the time because history has taught them they must hide their horns to be safe from people who might wish to trap them and use their magical powers.
In the snow they are very well camouflaged being white, which is why many took the safety of the frozen and glacial areas of the other lands in which to be safe.
In Perpetua the Unicorns are friends of Litrasaurus. He knows that they are not just horses, wonderful though horses are.