I'd change a lot of things and change them a lot i would. BUT working on a completely new piece will be more fun for you i think and probably more efficient too. I'll just list a few things you could consider.
-You plotted perspective for the bridge, but didn't continue it to include the castle, it's now really out of place. Add the perspective to the castle too.
-The camera angle and placement doesn't contribute to the theme. It would be far more efficient if the camera was looking up to the monster at a similar level as your character. In the future pay attention to the camera in your scene. Is it with your character or overlooking him and so forth.
-Your character doesn't seem that scared really, especially the smaller one. Act scared yourself and see how your body reacts. Shoulders go up and your chin might go to your chest if you're sort of hiding or in this case the head would look up with the mouth open. For the portrait you really should think what's inside the head. There's just two big pieces moving so it's not that hard. A little practice will make your heads way better.
-Now for the demon guy. Can you think of things that makes a character scary? I'm sure you can. Study WHY rosse's and rabid's demons look so malicious. Rosse's character has interest in the puny human, there's a lot of intent in the body language. Rabid's face makes it look sort of crazy with the asymmetric facial expression.
In a nutshell, try to be your character, study your own body language, look at other people how they emote and so on. In general it's healthy to keep asking "why" about things. Why do things look the way you do, why does a malicious monster look like it means business.
You should do a few studies of people, a few of landscapes and then make a picture similar to this in concept, but with all your newfound skills. Post whatever you study next in early stages so people can guide you through the whole process and give some pointers on things other than pixel-rendering.
Oh and, do have fun while pixelling
