Here's some stuff I've been working on. It started off with a simple biro sketch of a merman which I later developed in attempt to design one that's more anatomically viable than typical interpretations.

He's a soldier merman so I tried to make him strong with practical features such as starfish-like hands so he has better grip on weapons etc. I haven't explored many pattern designs yet but have the face down so far (settled for a hammerhead shape as it would be more practical for fighting).

^ I played around with different shapes to find something distinctive and appropriate
(most are ridiculous but you'll never know what might work until you try, right? ;P)
I liked the bottom right version too but felt it was too 'individual' for a loyal soldier breed
who would fight en masse and that it isn't as functional as the hammerhead shape.