The referee is responsible for deciding how monsters and NPCs react when encountered and what schemes and tactics they follow when the PCs are elsewhere.

When deciding how a monster or NPC acts, the referee should bear its level of intelligence in mind. Intelligent monsters might use any of the following tactics.

Traps and stealth: Monsters who are cunning but not physically powerful might lay traps or ambushes and may favor attacking PCs from a distance with missile weapons.

Guards: Monsters may use guards or pets to weaken PCs or protect important escape routes.

Magic items: Monsters will use any magic items in their lair to thwart the PCs.

Learning and preparation: If PCs encounter but do not defeat monsters, the monsters will learn from the experience and prepare for a repeat attack. They may build defensive structures, call for reinforcements, relocate their base of operations, and so on.

Adaptation: Monsters may copy or adapt tactics successfully used by PCs and plan specific counter-moves.

When designing encounters, the referee should remember that—like player characters—monsters and NPCs will join forces to increase their chance of survival.

Combined forces: Monsters skilled in melee, missile attacks, and magic may join forces.

Leaders: May have special abilities, maximum hit points, or additional Hit Dice.

The same as player characters, intelligent monsters and NPCs have their interests and motivations.

Role-playing: The referee should consider the monster’s reaction to negotiations with PCs, considering its alignment and personality. Monsters should not always cooperate with PCs’ wishes!

Allies: Monsters and NPCs may be encountered with friends, minions, or retainers. These will come to the aid of the monster or may avenge it if it is defeated.