Create another subclass of the Monster type. Call this one Vampire.
Override the terrorizeTown() method so that every time an instance of the Vampire type terrorizes a town, it adds a new vampire thrall to an array of vampires on the Vampire type. This array of vampire thralls should be empty by default. Terrorizing a town should also decrement the town’s population by 1.
Last, exercise this Vampire type in main.swift.