just a thought

The monster in the front seems to be off-centered and is throwing my eye a bit too much. also, change up the orange monsters in the background b/c they are very cut-and-paste.

you need to work on this a lot more. all your three monsters are essentially the same drawing, all you've done is change the main colour and size.
the mouth is also not well drawn, you don't seem to be that confident with the pen tool. i'd suggest drawing this by hand, scanning, and then working off that.