What is the scale of your game? How big are the characters (if there are any)? The details on the rock and the ripple size make it look fairly small (smaller than a person), but its pixel size is very large, I'd be surprised if you made pixel art character sprites to match.

The rock looks good overall and has an interesting shape, but I think you can make it look even better.

The colours look rather dull. Consider adding some faint hints of hues and hue-shifting to it instead of using pure grey. It's in blue water, so presumably the sky is blue, and this would affect the colours of the shadows.

The highlights are inconsistent, the white light seems to be coming from all directions. I'd also use those edge highlights you're doing more sparingly, as overused, they make the rock feel flat.

The details seen through the water look rather noisy, lots of single pixels that don't communicate any meaningful detail or texture. Similarly, the details in the big crack at the top of the rock look rather noisy. Pixel art is often about committing to strong shapes, because it can't communicate tiny details well. Try to focus on showing the big shapes, they're what will create your visual interest. Don't worry about the small details so much.

The shadow cast by the rock seems rather like an afterthought, it lacks the lovely shaping of the rock itself. The shadow would be a great opportunity to suggest some texture of the ground beneath the water without actually drawing it.

Lastly, the piece feels a little rough because of how you've placed thin dark lines immediately next to light shapes, making the pixelated boundry between them stand out more. Some anti-aliasing or different placement would really help make the piece feel more polished.

Here's an edit incorporating the above. I focused mostly on the big shapes making up the rock, and making more "details" by adding more protrusions and dips, rather than surface details.

I like the character style, but the motion feels unfinished since the character never finishes their step forward and there's no overshooting or any secondary motion to give the attack any force.

Depending on the character's personality, you may also want to keep their eye visible in all the frames. Expected fighters generally keep their eyes on their opponent as much as possible instead of twirling unnecessarily.

Instead of just thinking "I need a background for this level", think about where your game takes place, and what one might naturally see in such a location. Treat the backgrounds as an opportunity to show the player more about the world, establish the mood, etc. You could even use the backgrounds to help tell the game's story, if it's got one.

That is to say, don't limit yourself to just bricks. Build the whole scene. It's more work, but it's the kind of work that makes a huge difference to the player.

Gunpog's advice is good!

If you're not already, do warm-up wrist stretches before working sessions, including after long (hour+) breaks. Note, however, that the stretches you should do differ depending on whether you already have pain, preventative-care stretches can make the situation worse if done when your tendons are already inflamed or hurt. If the pain is serious (e.g. consistent, and/or accompanied by numbness in any of your fingers), it's recommended to not do stretches at all, and rest until your wrist heals.

However, no matter how ergonomic your tools are and no matter how good your stretch habits are, working for 15 hours a day will cause damage. You must find ways to reduce the time you spend working! In addition to being better for your hands, a reasonable work schedule helps prevent burnout.