I am very impressed with your use of texture and layers. Having all of this bitmap and transparency really pulls the piece together. The color palette feels relaxed and full of doom, pretty creepy.
I love the use of bitmap in the background, though, I think it would be nice to see the yellowish chunks in the back a bit brighter. I really like the clown space guns: the color choice is good and it has a good amount of depth. I feel like the opacity on some of your objects needs to be pushed up a bit more. Everything is transparent, so all of the objects kind of blend together. Good placement of text.
I love the textures that you used behind everything in this piece. While your character isn't totally terrifying at first, I think the color palette does a lot to give you the feeling you need for this piece, as does the swirl in the background. It also looks like you've really got the hang of the pen tool, which is awesome - your illustrations are looking really nice and crisp. I think you could probably move the text away from the two edges just a little bit on the sides where it says "killer klowns" - maybe take it down to about 75%of the scale that it is now, that way it'll also focus us on your character first - then the type, then the rest of the information. Thanks for putting in the additional information at the bottom as well - It's pretty funny that the whole cast is a klown. The last thing to consider is possibly giving him some hands so someone isactually holding the ray guns? I wonder if that would make him feel more menacing? I'm not sure if you wanted him to feel like a floating head with rayguns? I'd be worth a shot. Oh - and It would be great to either crop the guns a little more- or bring them into the art space so they don't get chopped right at the tip of the ray gun! Overall, I think this is great. I think you did an awesome job using all of the techniques and creating a creepy poster. Thanks!!