They all look really nice! But I'll judge them only by the design.

I slightly prefer the first, the fifth and the last one, because they are very particular, and nicely tought for the fifth one.

The first one is just something I've never seen before.

The second is ok, but the circular finger look abit of a forced design. The tail is great.

The third is good too, but nothing special.

The fourth one doesn't give a clear message or meaning. I'd really like to hear the insipiration or the meaning!

The fifth one has a simple design, but well tought!

The sixth one is the same as the fourth. It looks like a shark but... I don't know, it's hard to guess what's special.

The seventh one I think its the worst. Of course, not that negatively but still. It kinda remind me of the Little Mermaid's villain. Could have been something cool by the way, like making her look like a whale or something.

The last one is great! It's weird, misterious and nothing like a humanoid creature.
This thing shouts "I'm not anything you've already seen before". It really catches the meaning of the mythical creature of the mermaid.

In the end, you have made a great job! Character design is fun as hell, and seeing your soft style applicated to YOUR characters, it's just heartwarming.

Keep going on making these! I don't care if they are ugly or not special enough, thats the beauty of immagination!