@yuriqart! Hi, man!
This is pretty cool! What makes an artwork stick is often times the idea, not the technical side of things, so while it could use a bit of work, the idea is there and it is fun and memorable.
I've taken some time to do a quick overpaint with a few suggestions. Just a couple of little ideas and changes that popped into my head when I saw this image.
So the first thing that I see is that your light direction seems to be a little inconsistent. Looking at the shadow on the creature and the boys head, the lightsource is somewhere on the right, in front of the scene. Yet you painted the monster's left hand like it's being lit from a different direction. I fixed that.
Also, I adjusted the light on monster's head to match it with the boy and the arm behing him. In the original, it looks like monster's head is being lit at a slightly different angle.
Speaking of his head...
I just looove the furry texture you used on monster's arms. I realy think that something like this should happend on his head as well! Adding this furr texture there not only makes it look a bit more interesting, but also adds some unity to the design. Also, by making the creature's head more round I echoed the change that you did to the boy's head. You can achieve some great harmony through shape repetition like that!
Watch out for the boy's skin! Skin is actually a bit translcent, that is why we can see a LOT of warms in it. Those cool, desaturated colors you have used make the skin look very...dead? I guess that's a good word.
So as long as you don't want your kid to be a zombie, throw some warms in there!
I also adjusted the shadow that is being cast by creature's head. It works AMAZING as a compositon tool, since it leads our eye straight for the boy. However, with such a hard edge, this shadow calls A LOT of unwanted attention. You can push it back by allowing it to melt away. Make a grad in there, soften the edge the further away from the head it goes... Shadows do that in real life, you know? The further away they go from the object, the softer they get.
Here! I took a photo for you!
This is not a thing that is set in stone since the strength of this effect depends on the strength of the light source, but this image is a perfect opportunity to use it!
Last but not least, I made a color change to the background.
It is VERY subjective so treat it with a grain of salt, but I because the local color of the monster's shirt was sooo similar to the color of the background, I couldn't figure out the character's silhouette at first. Making a change like that will help the picture to read better. The green I used there is random. You can use any color you want
That is all I could think of at the moment.
This is a good picture though! It has some nice composition, a fun idea and I REALLY like how you've painted the boy's clothes. Good luck with your artwork!