The creatures encountered in an adventure set the tone for the game. They should be appropriate to the genre, but still a surprise for players. GURPS Creatures of the Night, Vol. 2 provides the GM with an assortment of territorial monsters, animals, and unnatural beings.
They defend their nests, build magic patterns on the ocean floor, and transform anyone who comes too close. They take control of the area around them, swinging from the darkness to attack intruders or altering the weather to distract innocents. They are easy to avoid . . . if you never come close to their territory.