well , i know its a total cliche , and well quite sissy
but i have to mention the unicorn
pass all the "omg girls , unicorns r cool"
they have been there , in fiction and fantasy,and also real life rumours since a s early as the 10th century , maybe even earlier , people have discovered dear with one horn , possibly pre-birth mutations , so same thing could have happened to a horse , or a hybrid and maybe the mutation didnt make the creature infertile (in most case mutartions do) ! myth or science , we may never know.