I always find little kids dressed as Chucky hilarious. I had drawn him as that already in last years Halloween comic, but the only other small horror character is Sam from Trick 'r Treat and I didn't want to hide his face.
Jigsaw was the perfect shape and color for Vincent, although I loathed drawing the trike!
I wanted Freddie in there as he's a classic, plus cats and claws! The stripy top made Fran a natural choice and realizing that I could draw her fur burnt sealed the deal!
I thought about Jason for Dad Cat, but honestly, J and I find slashers a bit dull. J demanded to be something cooler. The character design on the new Pennywise is top notch and the top heavy silhouettes of both characters worked. On my first pass I made the mouth too big, but I noticed the mistake on the neat pencils and he looked WAY better with the smaller mouth.
Lighting them all from below added to the creep factor. I wasn't exactly sure what to do for a background so I googled some horror movie posters and noticed that a green/blue smoke was common. I was having an issue of the blacks on Vincent getting lost in the colors behind, so I put some of the smoke inbetween the kids and the parents to add depth and help pick them out. As a bonus, the bright ground smoke ended up making the up-lighting seem believable!