I like how this came out, Nicely done! I take it rosalina with be your favorite smash bros character?

Also, I have a question. Would it interest you if I helped give you some pointers on shading and lighting?
I'd like your permission first before criticizing your work. It isn't bad, really. I just think you have more potential

Alright, this will be really long Lol

I'll start with the shading, you're using a good technique as is; gradient shading. however, it's confusing determining where the light is coming from. From what I can see. it looks like the light is shining above rosalina. but it gets a bit confusing because the back of her left hand, her visible cheek, and the left side of her crown is lit up signifying that some light is shining in from the left of the screen, whereas the left half of her dress is dark (I also see some light on her right sleeve as well yet her hair curls on the right happen to be darkened.) the shading and lighting is coming from about 3 different directions. the most logical direction I can see it coming from is from above (and some to the left). a technique that you can use that should help you would be to draw a light bulb before drawing your picture or before adding shades. you can draw a light blub, a sun, a yellow or white blob, anything that symbolizes the source of light in your picture. place the source of light in any direction you desire you have light shining down on. then draw/shade your picture corresponding to the light

For example, Im gonna say that in this picture, the light source will be on the right side of the screen, keeping the lighting and shading on her left hand, the lighting on her bangs, face, shoulder/collar bone, and crown. Then I would add some more lighting on the left side of her dress beside her wand and a little shade on the right side of her right arm sleeve, and her hair curls by her eye. as those are pointing closest to the direction of the light source, anything blocking, or away from the light source should be darkened. such as her folded forearm, holding the luma ( unless the luma is illuminating ) the hair curls on her left side, the left side of her right arm sleeve, and the left torso.

also the light reflecting off the jewels of her crown should be facing the direction the light is coming from (the right)

Another thing, you should take into consideration are the other sources of light, such as her wand, and the luma.

with her wand, you don't necessarily have to add too much lighting anywhere else. but since it's glowing, you could add lighting to he left arm elbow and part of her dress that the wand is closest to. I would use that blue color you used for the wand's aura, and lighten up just a tad bit, and decrease the opacity to less than half, using the middle brush, medium size, and apply it to the elbow and the end of her dress to show that the effects of the lighting.
for the luma, I would outline the left side of it with a close to white, yellowish color, remove the shading on it's arm, and legs, and give it's entire body a glowing texture by using the second brush with half opacity, medium large brush and select a color lighter than the luma's body color, but not too different. then add some shade to the right side of it's face where rosalina's hand is covering it, at the same time you can add a shade of yellow to that hand and part of her hair face and shoulder. just a tab bit of lighting. that would give the luma properties that they are emitting light.
one last thing, the grass. this should be simple, since the light is coming from the right. chose a light grass color to start with, and as you progress to the left side of the screen use darker and darker shades of grass.

Now, This is still a good picture, I don't want it to sound like you did poorly. Correct use of lighting and shading will make a picture stand out. even if it's already a good picture, it will stand out even more. It's like a puzzle in a way.
If i downloaded and reshaded the picture for you, I could show you, unfortunately, that is impossible to do here... (well, its not unfortunate because this prevents thieves)
but yeah, sorry for the wall of texts XD

Exactly. Also, I meant to say that one of your previous pictures, The "Wip2" picture of the girl in the cape has a good source of shading. I can clearly see that the light is coming from the right of the screen.
for some other tips, there's a "safer" way that you can go about shading and lighting. I notice when I press the playback button, you apply shade on the layer you add color on, instead of that, you can open a free layer to overlay the color. (after you finish adding your mono coloring) This way, you can shade over top of the objects without having it fused already. this makes it easier to shade and not worrying about it being on the picture. I know the Undo button is for that reason, but having the ability to make small erasings and edits without messing up the dress or having to simple press undo every time you mess up some where (and even sometimes, the undo button takes long to respond.) makes shading and lighting that much easier. after you're finished, you can merge the shadings with the picture.

If you have trouble determining where the light is coming from/where it should shine, you can draw a diagram. What I use to do was draw a blank character. no face, hair, clothes, nothing. then draw a light source. I will put it in the top right corner. Beneath that source I will draw a ray(field) of
light,as it passes over the character. the light source and light ray would look something like this " >o " the ">" being the ray of light, which gets wider as it passes along and the "o" being the light source. make sure the character is in between the ">" lines after you get that straightened out. draw arrows withing the light ray, pointing down to your character. not much, just about four or five. draw one past the head, shoulder, torso, waist, and legs.. the arrows should pass though the entire character. the arrows act as a guide. from the beginning of the arrow. that will be the brightest end, and to the end of the arrow, will be the darkest. anything hidden or facing AWAY from the arrows drawn down from the light source should be shaded as well, such as the back of your legs and arms, underneath your chin, and your hands, (depending of where its facing)

you seem to already have shading in creases, folds, and dark spots/zones down so that's good.
just focus one where the light is coming from, and how many light sources you have.