Yesterday, I introduced the concept of monster Motivations as a way to help understand how to use that monster when designing encounters, or what they might be working toward when encountered as wandering monsters. But motivation only explains what the monster wants. Disposition, on the other hand, is a way to help understand the general attitude of the monster, and how they interact with others. This again is because alignment alone (even dual axis alignment) doesn't really help a DM in knowing how to play a monster during encounters.
Many of you may have seen the alternate Reaction tables I created (that appear both in Petty Gods: Expanded Edition and RS1: Fang, Faith, and Legerdemain B/X Rules Supplement. The idea is that Reactions table can be created around Dispositions, with extremely good and bad reactions stemming from that Disposition. E.g., a bad reaction from a Passive creature shouldn't be the same as a bd reaction from an Aggressive creature. Below is an example of a custom Reaction table around a Passive creature (the Álainn, from the Creature Cache).
You'll see there's a noticeable correlation between many of the alignments and the Dispositions, but there's a nuance in some of these Dispositions that alignment doesn't capture (e.g., consider the differences between a True Neutral animal that is Aggressive vs. Passive, or a Lawful Good humanoid that is Friendly vs. Passive, or a Chaotic Evil fiend that is Aggressive vs. Manipulative.
DISPOSITION provides a general reference for the way a monster of that type typically interacts with other creatures around them, though it may vary among individual creatures of that type. Disposition is the main factor when determining a monster’s Reaction during an encounter. Following are the standard Dispositions, though the DM may develop their own.
Friendly. Friendly creatures will generally approach other creatures optimistically, unless they know those other creatures to be dangerous or hostile. Furthermore, friendly creatures with a greater intelligence can often be counted on to help the PCs or offer them assistance in some way.
Passive. Passive creatures generally prefer not to interact with other creatures, and rarely (if ever) attack. If attacked, they are more likely to flee (if they are able) than to engage.
Indifferent. Indifferent creatures have as much likelihood to interact with other creatures as avoid them altogether. They generally won’t take interact other creatures unless approached, provoked, or otherwise engaged.
Ambiguous. Ambiguous creatures are not prone to any particulary behavior, or they have unclear intentions. They are unpredictable and may act in in a number of ways, depending on the situation.
Rational. Rational creatures are unemotional and considered. They will take their time to examine the parameters of a situation before acting or reacting (if the situation allows).
Aggressive. Aggressive creatures are typically short-tempered, acting with hostility and arbitrary violence, spurred on by greed, hatred, vengeance, or bloodlust. They are likely to attack on sight, though more intelligent creatures of this ilk may weigh their chances of success in combat before engaging opponents.
Manipulative. Manipulative creatures are possibly the most dangerous of all the disposition types. They rely on cunning, guile, and deceit to achieve their goals, and may act in almost any of the manners outlined above. They are unpredictable and sometimes downright devious. They may simply be mischievous or they may be driven by darker goals. They may pretend to be an ally, only to turn on the PCs later. They may use their charm and persuasion to influence the actions of those around them, possibly even getting the PCs to turn on one another. They may even resort to intimidation or aggression if they think it will work. There is little a manipulative creature won’t do if it helps them achieve their goals.
