Realistically, the only thing I can Imagine is asking or removing particular classes of monsters and maybe introducing Stat caps to ensure no one monster goes out of control. For example, Melee gobs have low HP and damage, but Ranged goblins have higher Damage and lower Health to get you started. Then Orcs have more bulk and their leap, but are generally slow. Werewolves can be ambushers who hide then pounce, minotaur can be slow, costly, Melee units with high damage and bulk but horrible range. Salamanders can be living cannons firing AoE fireballs from afar, and tentacles can coat your barricade and catch one woman who slips past for free every now and then in exchange for eggs, but consume the caught girl, preventing you from abusing them without sacrifice, and consume more eggs as the caught woman gets stronger.