If they ever decide to make a animated or live-action horror film based on characters from Pokemon, the person who made these terrifying versions of Haunter, Muk, Houndoom and Solosis should definitely be leading the project, or at least use his concept art.
Snook-8 took a handful of Pokemon, most of them not the most popular and known in mainstream, and simply took the kiddie factor out of them, turning them into the stuff nightmares are made of.
The scarecrow of the Pokemon world.
For the complete gallery of scary looking Pokemon, check it out here. For more Pokemon alternative art, here are some awesome drawings giving Pokemon a more realistic, down to earth look.