Role list in the Coven lobby says that there is a guaranteed Mayor, however in-game role list says that there ISN'T a guaranteed Mayor, and instead replaces him with a Random Town slot.
In-Game role list: https://gyazo.com/4f5576f2720acc2ae815f28b33d7b7fc
Lobby role List: https://gyazo.com/befad5b6afeb68ce1e2950736c4d6d0c