So I started working on this for the genre bending challenge, but it doesn't seem to be working out.  The monster on the left looks kinda weird and I can't figure out how to shade it.  Not sure what would make it look better and match the creature on the right...  any help would be appreciated!

First, look at the monster on the right. You have big areas of single colours, most notably the belly, followed by smaller areas of shadow, also of a single colour or of only 2 colour dithering. This works very good: it gives a good idea of how the light works and adds depth.

Now, the monster on the left is very different: you start straightaway with the dithering. This is why the green monster looks 'noisier' than the purple one. You should probably do as you did with the purple monster: choose areas that will be in a uniform shade of green and start dithering and darkening frther away from the center of picture.

Hope that helped.