I've always been intrigued by the paranormal, and the Pokemon games have their share of spook in the form of Ghost types.
Ghost types are super effective against Psychics and other Ghosts (for some reason). They are weak to Dark and other Ghost types as well. Due to a glitch in the first games, however, the Gastly line (being the only Ghost types that generation) were weak to Psychics due to their Poison secondary typing, making them difficult to use.
Some of my favorite Ghost type moves are Shadow Ball, Shadow Claw, and Hex.
Favorite Pokemon of this type include Aegislash, Chandelure, Golurk, Trevenant, Froslass, the legendary Giratina, and Gengar, who tends to find his way on my team all the time.