Pink, welcome to the world of spriting. I am excited to see that even though you are only on your second? fusion, you are already bravely venturing into the art of scratch spriting. Since my expertise is in scratching, and I try to encourage people into doing more scratch spriting, I'll offer my critique on the nifty little hand you scratched for the graveler sprite. While this was a good start, there were a lot of errors, so I'll go step by step.
1. The colors you used are different than the colors in the rest of your sprite. I don't know where you got those yellow and gray hues, but they aren't anywhere else in your sprite.
2. The outline is too thick where it becomes slanted (the top of the middle finger and the bottom of the palm). Remember, always make outlines one-pixel thick, which means if you have a slanted outline, you shouldn't have adjacent pixels.
3. The tip of the middle finger is too small, too round, and the outline is too dark. The lower finger is also a bit too thin. Graveler has wide, oval shaped finertips. Separating the fingertip from the finger with a black outline makes the fingertip look flat and completely disconnected from the finger. Instead, you should use the lighter outline color and even the shading color to gently create the crease that separates fingertip from finger.
4. Your outline colors dont match the shading. Rule-of-Thumb: any outline that is facing towards your light source (top-left), and isn't shaded from the lightsource should be colored with something other than black. outlines that are shaded from the light (bottom-right) will be black.
5. The wrist is too thin. It actually looks like the arm ends before it reaches the back of the hand.
Here's that same hand in which I edited the mistakes. It's not perfect mind-you, but I think you can see the difference and where the differences are.
I hope this is useful for you. I'm always willing to help anyone brave enough to attempt scratch spriting. Keep incorporating scratching into your sprites, and soon you'll be scratching out whole sprites from nothing.