[@RaeoftheLight]If we are talking strictly appearance, then they have two forms
1) The butterfly
2) The spirits true form. Whether it be humanoid, animal, half-breed or otherwise

Like this! It's only limited to your imagination ;)
[img]https://s-media-cache-ak0.pinimg.com/736x/4f/2c/9e/4f2c9eb678f3d5fd5b3ca319846f4d37.jpg[/img]