There are two cases of pursuit and evasion of pursuit. The first is in underground situations, and the second is in outdoor settings. There are various special circumstances which pertain to each case, so each will be dealt with separately.
When player characters, with attendant hirelings and/or henchmen, if any, elect to retreat or flee from an encounter with a monster or monsters, a possible pursuit situation arises. Whether or not pursuit will actually take place is dependent upon the following:
If the matrix or key states that the monster(s) in question will pursue, or if the Monster Manual so states, then pursuit will certainly occur.
If the monster or monsters encountered are: semi-intelligent or under, hungry, angry, aggressive, and/or trained to do so, then pursuit will be 80% likely to occur (d10, 1 through 8).
If the monster or monsters encountered are of low intelligence but otherwise suit the qualifications of 2., above, then pursuit will occur with the following probabilities:
a. If the party outnumbers the potential pursuers, then pursuit is 20% likely.
b. If the party is about as numerous as the potential pursuers, then pursuit is 40% likely.
c. If the party is outnumbered by the potential pursuers, then pursuit is 80% likely.
d. If condition C. exists, and furthermore, the potential pursuers conceive of themselves as greatly superior to the party, then pursuit is 100% certain.
Pursuit will have 3 separate cases:
1. The pursued are faster than the pursuers: Unless there are extenuating circumstances, such as a ranger NPC or an invisible stalker or a slithering tracker pursuing, then pursuit will end as soon as any one of the following conditions is met:
The pursued are in sight but over 100 ft. distant; or
The pursued are out of sight and were over 50 ft. distant when they so left the perception of the pursuer(s); or
Pursuit has continued over 5 rounds, and the pursuer has not gained perceptibly upon the pursued.
2. The pursued are of equal speed to the pursuers: As in case 1. above, pursuit will end as soon as any 1 of the following conditions are met:
The pursued are in sight but over 150 ft. distant; or
The pursued are out of sight and were over 80 ft. distant when they left the perception of the pursuer(s); or
Pursuit has continued over 1 turn, and the pursuer has not gained perceptibly upon the pursued.
3. The pursuer is faster than the pursued: The pursuit will be broken off only if one of the following occurs:
The pursued are out of sight and were over 200 ft. distant when they left the perception of the pursuer(s) ; or
The pursuer is unable to continue due to reasons of physical endurance.
There are several circumstances which will affect the pursuer. These are:
Barriers. Physical or magic barriers will slow or halt pursuit, i.e. a locked portal, a broken bridge, a wall of fire, etc.
Distractions. Actual or magic distractions will be from 10% to 100% likely to cause pursuit to falter or cease altogether. For example, a dancing lights spell moving away from a fleeing party which has extinguished its light sources might distract pursuers, just as a phantasmal force of a strong helper joining the pursued might cause the pursuers to cease pursuit. Similarly, if the pursued passed through or near some other creatures which would be hostile to the pursuing force, or at least not friendly to the pursuers, then it is quite possible that the creatures passed through and the pursuers would become embroiled.
N.B.. The likelihood of any distraction being successful is a matter for individual adjudication by the DM, using [1.25] principles and common sense as they apply to the particular circumstances prevailing. There are also 2 sub-cases here:
Food. Food, including rations and/or wine, will be from 10% to 100% likely to distract pursuers of low intelligence or below, providing the food/wine is what they find palatable. Roll a d10 to find the probability, unless you have a note as to how hungry or food-oriented the creatures are. Add 10% to the result for every point of Intelligence below 5, and give a 100% probability for non- intelligent creatures pursuing. If probability is under 100%, roll the d10 a second time, and if the result is equal to or less than the probability determined, then the pursuers break off pursuit for 1 round while the food/wine is consumed.
Treasure. Treasure, including precious metals, gems, jewelry, rare stuffs such as ivory or spices, valuable items, and/or magic will be 10% to 100% likely to cause pursuers of low or greater Intelligence to be distracted. Pursuers of low Intelligence will have an additional 10% per 10 items (regardless of actual value) dropped, i.e. 20 copper pieces have a 20% additional probability of causing a distraction. The value of items dropped, known or presumed or potential, will likewise cause pursuers of average or greater Intelligence to be more likely to be distracted. For each 100 g.p. value or potential value, add 10% to base probability. Roll the d10 a second time to see if potential and actual interest are the same, just as is done when food is used as a possible distraction. (Note, however, that very small items of value - notably, gems and the like—would have a chance of going completely unnoticed in the heat of pursuit.) If success occurs, the pursuer will be distracted for 1 round, or the length of time necessary to gather up the treasure, whichever is the greater.
Multiple Choice. It will most often come to pass that the pursued take a route which enables them to cause the pursuer(s) to have to make decisions as to which direction the pursued took in their flight. Thus, at a branching passage where there are 3 possible ways which could have been taken, there is a basic 2-in-3 chance that the pursuer(s) will take the wrong passage. Likewise, if there are a door and a passage, there is a 1-in-2 chance of wrong choice. This base chance assumes that the pursuer cannot see the pursued when choice is made, that sound does not reveal the direction of flight, that smell does not reveal direction of flight, nor do any other visual, audial, or olfactory clues point to the escape path. As DM, you will have to adjudicate such situations as they arise. The following guidelines might prove helpful:
Light. Straight line of sight is near infinite, any corner cuts distance to 60 ft.
Noise. Characters in metal armor can be heard for 90 ft., hard boots can be heard at 60 ft., relatively quiet movement can be heard at 30 ft.
Odors. Normal scent can be detected by creatures hunting or tracking by scent for several hours - even in a dungeon setting. Scent con be masked with various things - mustard powder, oil of citronella, crushed stinging nettle, etc.
Building Interiors. Treat these settings the same as one underground, as applicable.
If it is discovered that a pursuit situation exists, and the player-party elects to evade rather than confront pursuers, then record the relative speeds of pursued and pursuer. Move the pursued party as many 10’s of feet as their slowest member is able to travel, and likewise move the pursuing party as many 10’s of feet as its fastest member can travel, noting positions of slower members, if any, as well. This movement is accomplished on the map, of course.
Three such movement phases are (for game purposes) equal to 1 round.
At the end of any movement portion where any number of the pursued party is within 10 ft. or less of any number of the pursuing party, confrontation must take place between the concerned members of the parties. (At this point the remainder, if any, of the pursued party may elect to stop flight or continue evasion attempts as they wish.) Also, at the end of each movement portion it is necessary to check the 3 separate Pursuit Cases and any Modifiers to Pursuit to see if the pursued party has succeeded in evading the pursuers. Keep track, not only of the route of flight, but also of the amount of game time so spent, as some pursuit will automatically cease after a set period without confrontation.
Mapping During Flight. No mapping is ever possible. Give no distance measures in moving the pursued. Give no compass directions either!
Pursuit in the outdoors is generally similar to that in settings underground or indoors. The 3 general rules of likelihood of pursuit apply. However, pursuit will certainly continue until evasion is successfully accomplished.
In outdoor settings, evasion is accomplished in a different manner, the variables being the relative speed of movement and size of the parties concerned and the type of terrain over which pursuit takes place. Available light is also a factor.
Upon encountering creatures from which the player-party flees in order to evade, determine if a condition of Surprise exists.
If the player-party has surprised the creature encountered, evasion is automatic.
If no surprise exists, then follow the procedure below. If the party encountering the creatures is surprised, then no evasion is possible, and confrontation is unavoidable.
Find the chance for evasion by adjusting the base chance according to variables.
The pursued party rolls percentile dice, and if the number generated is less than or equal to the adjusted base chance of evasion, then they have had immediate success at eluding the pursuers.
Otherwise, pursuit continues unless the pursuers are faster than the pursued and can close within 1 hour, in which case confrontation must take place.
Continuing pursuit requires on evasion check every game hour. After the initial check each game hour, another must be made just as is initially done, with the added stipulation that any result of 0% or less indicates immediate confrontation and no further chance of evasion.
[See also Appendix A—Conditions, Fatigue & Exhaustion]