@rcartwright +1 to what tess already said, but I would also like to add that I think the snake could be more of just a silhouette. It will still be obvious as to what it is (though I would push the head to the right slightly to not cause a tangent with the wood) and that would help give it a more ominous feel. I would suggest that you try out a few lighting and color schemes, before you push into building it up to achieve the effect what you want. I just noticed the village in the scene and that would be a nice source of lighting for the scheme if you wanted to go for more of a night scene with an orange/blue feel.
Could you explain the scene a little more? Is the frog just training and the other animals are sneaking up on him or is he getting ready to fight the snake? If it's the former then I would have him not noticing any of the other creatures and in more of a closed eyes, spiritual expression. If it's the later then he could do with a more intense look on his face and the pose could be more dynamic (as it is, he looked like he may fall over to the right. At the moment i'm not getting whether I should be worried for the frog or cheering him on for an awesome impeding fight.
Not sure what the purple things are, but I kinda like them if you are going for making the forest a scarier place and as @TessW said, pushing a purple color scheme in the shadows may work nice with that if that's the way you want to go, although I would move the purple thing that is right in the middle as it's doesn't seem like it's a major point, but it catches my eye more than it should.
I know it's yet to be finished, so I hope you don't take my comments too harshly, there looks like there is a lot of potential in this piece and I'll look forward to seeing future updates 
Good luck with it