Arkan Sonney

Except from Encyclopedia Mythica:

The fairy pig of the Isle of Man. It is usually described as white with red ears, and is able to change its size at will although not its shape. The fairy pig is believed to bring good luck when caught, although catching it is very difficult.

...yes, I was in a "draw an uber-obscure mythical animal" mood again. Also, hey, I don't draw enough piggies.