Dobhar-Chú -- fascinating. I wonder if that's what Susan Cooper was thinking of with those black -- were they minks? I forget -- in
The Grey King, one of
The Dark Is Rising series. (Anyone who likes Arthurian/Celtic mythos should read those; they're books for young adults but work for all ages.)
danrak -- I have an interesting anecdote. Two of my friends were driving a winding country road in northern Delaware one night, out in a forested area. A white dog ran across the road right in front of their car. Its eye glowed green, and the passenger remarked on how odd it was that it was reflecting towards the car at that angle -- normally, dog eyes reflect when they are facing a light source. Then the driver said she thought it had weird markings, because it was all white, except that it had reddish-brown ears.
At which point my friend who was the passenger told her to be very, very careful the rest of the way home!
I'm afraid my favorite animal has been a unicorn since I was very small, but it was always a black unicorn with bat wings and an obsidian horn like a scimitar.
No, I'm not Goth. There was just a unicorn like that in a beautiful illustrated book called
In Pursuit of the Unicorn, and I though that looked much more interesting than the shining and pure and pretty ones.
As for other mythical beasties, I think I'd have to go with the
Giant Carnivorous Furry Ants mentioned by Herodotus.
(He actually got
half the story right, but it had obviously been embroidered by the time it reached his ears -- according to his version, the giant gold-digging furry ants were very fierce and would eat a full-grown camel. )