Wow...
I think the hanged dude should be a robot. That would be sweet.
lol.
Yeah, have a kind of racism towards the mechanical men theme. Like Animatrix.
I agree that the purple dude looks out of place. You should just make a single character, and base all the other characters in your layout in that style, with similar pallette choices and proportions, but different poses and clothes. As I said before, I like the grass, but the layout would definately benefeit from more. A hellhound, pile of corpses, and some silhouettes of more hanging people in the distance would add much to this. Again, as I said before, the tiled look should be lost. Go for an approach as if this were a single piece of art, not a game. Games use tiles - small segments of art. Works of art are unique in every section, unless a recurring theme is sought.
Some small, shriveled plants, maybe?
If you're going to make the background more detailed, remember to add outlines to the sprites that you wish to be links.