Alisterror - The Occultist Pokémon (ghost/psychic)
“A ruthless, cunning Pokémon born from a life of neglect. It is said many inexperienced trainers have tried to pursue it, but never returned.”

original tumblr post (more info and bonus sketches)
part 1 (Hatbitty and Hatboo) | part 2 (Hauntbox)