I have an idea to name the kraken boss "ancient horror" or something like that.
And to pair with the boss, guarding the sunken temple, let's add some assassins and sorceresses from the Dungeon faction (like cultists).
Or, perhaps, mix creatures from Inferno and those very sorceresses; that would be more like cultists. But then, I'm afraid, there will be a problem with morality...
In general, it seems that you need to create another NCF creature.