For me they needed to be given a grungy look to make the creepy feel come to life you could however use these stamps in many styles of project. 

Here's What I Did:

I have created a wall hanging using That's Crafty! MDF substrates, this make uses a 4.5" x 9" panel with 3 MDF ATC's mounted on it. I started with each of the ATC's each got a thin layer of gesso on them before randomly applying paint using a brayer, I always use a brayer instead of a brush as it gives a much more random and textured effect and the layering of colours is so much lighter so the layer build up is more evident. Once happy with the background I then added further details by stamping with the paint and some stencilling. I added some torn washi tape and roughly drew around the ATC with a black fineliner pen. I then created the back panel and I started by covering with a piece of designer paper which I glued to the MDF with gel medium. I then gave the panel with the brayer treatment to match the ATC's not overdoing the paint so that the design of the paper still shows through.

Then back to my ATC's to add the characters, I stamped them onto mixed media card with Archival ink and coloured them with Zig Pens, the colours of these are very bright so once I had coloured them all I toned them down and made them look more grungy by blending Vintage Photo Distress ink over them. I've also added a bit of grey pencil to them to further grunge them. I then cut them out, edged them with distress ink and glued them to each of the ATC's. Before adding the 3rd one I used part of one of the sentiments from the Katzelkraft stamp set Batman to add 'Come to the Darkside' which I did by heat embossing with black embossing powder.

The final touch was to add the 'Snarky" saying which is from Tim's Snarky sticker book. I then gave the entire piece a covering of Vintage Distress Collage medium which further adds to the grungy look of the piece.