Here's a pencil sketch of what Finn looks like in horse form

In case you can't read it the words say:

• scar on right side
• eye has no real pupil

I know it's a tad disproportional to how a horse is supposed to be but please bear with me, I don't draw horses very often ^^''

The mane and tail are actually very fine strands of different grasses and such that grow underwater and in swamps. But from a distance they appear to be just hair.

To compare Finn with others here's a few more pictures of kelpies: