Inca: After some thinking about your painting, I've decided to not do a paintover. I think you can take it a lot further on your own, and I think you will learn more by doing some of the problem solving on your own. I'll cover some of the issues I see in your painting, but I want you to try and work on it without me painting over it. If you get further and find you get stuck or need help feel free to post it in this thread again and I'll help out.
So you say that you want a dynamic picture...and yet the first thing I see is about as static a composition as possible. Below I have shown you a simplified version of your composition--perhaps there you can see better why it is not that exciting. The painting is very symmetrical, and has the focal point dead center (and the focal point consists of two figures in the same pose both taking up the same visual space, and standing in the same spot). The horizon line is not pushed very far in any direction. The values are very similar overall (although this may because it is so early in the painting). There is no sense of foreground, middleground and background. In reality you have only a middleground, and this makes for a flat and static image. Right now the only thing you have going for the image is some strong silhouettes, but an image cannot ride on that alone. Imagine how good a painting it would be if it resolved all the other components I mentioned, and then combined with those strong silhouettes!
You need to choose one aspect of the picture and REALLY try pushing it. Do you want them to seem imposing? Make the horizon line SUPER low and use an extreme 3 point perspective. Or maybe you can choose one shaman you want to emphasize--make them much bigger and closer than the other one (this would be a good chance to add in some overlapping, which is one thing that is severely lacking in your painting and flattening it out). Maybe you want the image to have a lot of depth, so you can add in more of a foreground with some dead guys and show more stuff going on in the background. Perhaps you will decide this angle for the scene isn't what you want at all, and will change the image completely. I don't know. It's up to you. But you need to change SOMETHING to make it interesting.
Below is a screenshot from Kung Fu Panda 2. It's a similar sort of scene to your, in that the focus is on a character holding a weapon towards the viewer. But look at how interesting a shot it is. The hammer is so close to the camera that it appears bigger than the rhino, and barely even fits on the screen. This give a real "in your face" and menacing feel. Notice also how the horizon line has been tilted so it is no longer horizontal--this is an old trick called a Dutch Tilt, and is used to make static images more interesting since all the verticals are now diagonal and have more direction, and feel more "off balance" and dynamic. It is a good trick but can be overused, so be conscious of when you do decide to use it. Anyways, this shot is a great example of the artist(s) decided on one thing to emphasize and going all out.
In conclusion, you really should not be worrying about small changes in the pose and stuff at this stage (to be honest it took me a while to even see what the difference WAS). Focus more on the illustration as a whole, and how you want it to read and what you want it to get across. Sure, you can play with the poses, but make some major changes to them and see how it looks. Don't fiddle small things.