What do you think is the hardest combination of Ancient One and Herald to win the game?
Just for fun
Try Rhan-Tegoth with the Black Goat. At least your death will be quick! 
No, try Rhan-Tegoth with Father Dagon. Cultists mean doom tokens and a terror level increase, which strips off clues and usually means another doom token.
Although I could see Cultists making an appearance a bit more frequently with Black Goat...