Try speeding up the animation just a little. I really like the way the tail wobbles, maybe it just needs to be sped up a bit. What you could change is the tail finn itself, it looks too static because there's zero animation on it.

Also, the anti-aliasing you used on the tail's outline looks nice, why not use anti-aliasing on the rest of the sprite (eg. the arms) ? ( <-- that's a personal opinion though.)

You're welcome please post mermaid 2.0 here when you're done with it !
I've always used Gimp, I don't know if it's the most appropriate but for me it works very nicely for everything including animation (and it's even open source  ).

The green hair of the main character should have a darker outline (much like the two other guys), or else it blends into the background.

Should I tone down realism on the background? or there is no problem on keeping the background like so?

I like it as it is !

Welcome to the forum (I don't know if it's appropriate since I'm a noob as well but hey)

Your picture is pretty nice, especially considering you're beginning. Here are some areas you could work on to improve it :

- There are some anatomy issues with your mermaid : I'd make her waist less square and a bit hourglass-shaped, give her some feminine curves ; I'd make her "thighs" a bit longer so that it looks like her "tail fold" (errr...) is where her knees would be if she had legs, I don't know if you get what I mean. Don't hesitate to sketch your character on paper before going full pixel art.

- The animation isn't bad but looks a bit choppy. You could add some intermediate frames to make it smoother.

- The color count is super high (over 50), you have a lot of different shades of blue. You could easily make it work as well while reducing the number of colors. For example, the dark blue used for her eyelashes, you can re-use it for the shaded part of her tail. Always re-use an existing color instead of using a different one that's almost the same. Also, try not placing random single pixels as much, it makes your image look noisy.

- I love how you made her tail and the fish's tail see-through. I would give her mermaid tail a bit more depth by adding a slight color while keeping it see-through.

Real quick edit, with fewer colors, a bit more contrast, fixed her silhouette a bit, and the thing about her knees

Can you please recommend me some courses (other than the list on forum)

Since you've already learned some of the basics, once you feel a bit more comfortable I'd recommend this website (didn't see it on the list, if I just missed it then my bad), it covers some more "advanced" techniques that I found were of great help.

(Sorry about the long post)

Thank you, I'm glad you like it
I'd like to know if something's off about my animation though