Warlock idea I randomly came up with one night. They are a ghost train conductor, and their patron is the phantom express.

When the conductor uses Power Word: Kill, the foe hears the train in the distance. As they turn around every which way to try and find it, the train never shows up even though the whistles and chuffing get louder and louder. Only when it's too late does the train appear, taking the foe with it.