Kelpie

You asked for critique, so here comes mine.

Firstly, I am really impressed by the top half of the Narwhal/Hippocampus, the dappled skin texture looks very soft and smooth, like it belongs on the body of a Fish, and not a Horse. The texture also suits the animal very well, since the patterns look like underwater bubbles; linking the animal closer to its underwater world, thus increasing the aesthetics. In addition the eyes are done wonderfully; they look like they're made of rounded pebbles that one would find underwater. The final thing I love about this part of the creature's body is the webbed fins that replace the mane, I think that is a truly inventive bit of detail that does wonders for your animal.

Secondly is the lines of hair that are placed around the upper body. These patches of hair, bring more character to the animal and make him look like he has a wise, but kind personality. I can tell you've thought very carefully about the colour palette, because the hair has a similar resemblance to Seaweed, bringing in a mystical underwater touch. Overall it's a really pleasant feature you included.

Thirdly, is the bottom half, the transition between both parts of the body is very gradual, giving a graceful appearance to the Narwhal/Hippocampus overall. Many artists know the struggle of maintaining perspective. You have mastered it. There is a constant decrease in size along the tail, making it look thoroughly realistic.
Also, that twirly end of the tail is brilliant, nothing else needs to be said.

If there were any improvements to be made, I'd suggest that more of the hair is added beneath the chin to create a Goatee, which would look very fitting to me.

To conclude you should be very pleased with the outcome, I only wish I could create art as gorgeous as that. By looking at my ratings, you'll find that I think very highly of this masterpiece.