Hello Elie Ly-kok.
Nice image! looking good so far. For the environment, I would pay a little bit of attention to your lighting setup. Based on your BG, looks that the light is hitting from the top right corner. This works great with the BG castle, but I think it should also hit the right side of the cliff (it will feel more volumetric)
Also, pay attention to the FG elements like the rocks and the tree on the right side. Feels like their lighting dont match very well with your BG.
The Knight character can be very tricky to integrate because of the very reflective armor. The environment that is reflected on the armor doesn't quite match with the environment of your painting. Based on the current reflections, I am guessing the original environment of the character was an interior with probably big windows which are providing those highlights all over the surface of the armor.
To make it feel more integrated it would probably have to reflect the green grass around the legs and the blue sky on the metallic surfaces that are facing up towards the sky.
I hope it helps. Keep working on it, I think there is a lot of potential in this image!
Good improvements but I think you should still bring down the horizon a bit more. Textures on the main cliff in the left side looks a bit blurry and inconsistent in terms of details and lighting. Also the castle can be more grey tone to feel more photo realistic. You may also check the perspective of the cliff at the very bottom where hits the sea.
The very foreground rocks could help with more dimension and details and tree's light direction seems wrong. Over all I think if you move away from this warm to more cool dark grey tones would help. Game of Thrones could be a good reference for look and feel.
A lot of the edges are too soft, get rid of the knight, and create a mood of lighting, let the light draw us in as to what you are trying to emphasize, what story are you trying to tell from your painting. The fg rocks, knight, castle, sky, are all lit about the same as of now, therefore feels flat, and no meaning.
Don't just modify to look pretty, what are you trying to say first of all. Answer that first then you'll see you get good direction on your own.
Darken foreground, perhaps crepuscular rays falling on the castle's direction, with an overcast sky?
Also, how do people access the castle? Perhaps a bridge or pathway showing that, otherwise the princess has some rock climbing to do ;)
A sunset, with the sun coming right behind the castle would be nice, and would create a dark foreground for you, with backlit leaves.
At the moment it just looks like a regular tourist photo of a castle.
It's a matte painting, so tell a story, make it awesome, :)
So to sum up,
1. come up with a story
2. how do you express that story visually in your painting, (do rough concepts, thumbnails)
3. pick a lens, focal length, camera angle
4. drop a light into a your black scene
5. paint how everything reacts to that light as it does in the real world (use photo or real world reference as to how light reacts to the different objects in your scene, rocks, water, armor, leaves all react differently to the same light, don't paint based on what looks "cool" or "good")