Barriers Hinder Cooperation
A barrier can delay or bar a response to a disturbance.
Doors
A sturdy door might be sufficient to prevent entry to fairly strong opponents that cannot open doors. A barred door will delay opponents that can open doors. If the party can briefly spare one person to close the door after hearing animal noises from beyond it, then dealing with that threat can be delayed (and the party can choose to retreat safely for rest).
If the party does not think of closing/barring a door, the DM might decide that the animals flee rather than attack the party. This will warn others, who might flee, set up defenses, or marshal their resources for an attack. Prepared defenders/attackers will be more challenging, but the party will also have more time to defeat the current opponent and to decide whether to retreat or proceed with caution, knowing that the animals are not far away.
Do Not Enter the Fire Swamp
If the shortest path between the party and the main force includes a dangerous area, the main force might be substantially slowed, use an slower but safer alternate path, or choose to let the intruder pass through the dangerous area first.
- A passageway that recently suffered a partial collapse might be considered safer to avoid.
- A large area carpeted with patches of fungal growths that spew nauseous spores (very unpleasant and slowing but not longer-term harmful) would be avoided and traversed slowly by denizens even in an emergency.
- A path crowded with traps will not be rushed through to attack the party.
The alerted denizens might be waiting just outside the Fire Swamp, making that encounter more difficult. However, the party will be given the opportunity to recover from the previous encounter before entering the dangerous area, and the dangerous area might both induce caution in approaching the waiting enemy and provide information about a future encounter (e.g., day-old goblin vomit found by a patch of fungus).
The perceived danger could also be an outdated taboo or something much easier for the party to manage than the local residents. Even something as trivial as the light sources used by the party might reduce the danger — e.g., being able to see discolored stones or weak-sighted cave scorpions finding even lantern light uncomfortably bright.
Constricted Passage
If the shortest path to the main force is constricted, a response might be delayed in reaching the party. In addition larger creatures may not be able to use that path or be extremely slowed. If the one alerted by a disturbance has to traverse the constricted passage (audible alarms warn the attacker and the creatures might prefer ambushes) and the response then has to traverse that area, enough time might pass to allow the party to finish the earlier combat.
A section inhabited by small creatures might be impassable to a large creature. A somewhat playful use: a low-intelligence head warrior might use a growth potion ("Me giant now. Crush puny men.") only to be trapped in the more spacious areas or forced to crawl/worm through small passages. By the time this warrior is encountered, the potion's effect may be nearly over (and the DM can intentionally time it so that this happens). Even if the party encounters this warrior before the potion is quaffed, the party could still escape (a gigantic goblin crawling through a narrow passage will block the passage).
A wide crevasse/pit with planks set aside in another room might significantly delay the response to a disturbance. If the party scouted ahead, the scout might move the planks so that a response coming from that direction would be significantly slowed; leaving behind one sabotaged plank might be even more effective.
Variable Responsiveness
Fools Rush In
If the creatures alerted are intelligent, they may choose to meet the party in a more defensible position. They may also attempt to flank the party by sending a significant portion of their strength around behind the party. While Flanking is often good tactics, it also presents the possibility of easier defeat from divided forces.
Ambush predators will not rush to potential food and some humanoids prefer traps and ambushes.
It's Just a Rabbit
Even if a community fights as one man, bringing out the holy hand grenade any time one sees a rabbit is not normal behavior — most rabbits are not Killer Rabbits. For intelligent creatures, the initial response to the sound of combat would likely be alerting the community to give time for preparation and sending a significant but not especially powerful scouting force to handle the threat or at least determine its nature.
The expected intruders would typically be incidental wanderers (easy kill), conquering forces (organized response), or raiding parties (defend valuables). Commando raids are not the normal threat.
This is not as effective when the allied inhabitants are few (as the first response party would be most of the creatures anyway) and is not normal for creatures with a pack response (e.g., ants, wolves) or when all are relatively close and don't have to grab weapons much less don armor.
A Strong Defense Is the Best Defense
With an intruder, there is less expectation of spoil and more concern with being despoiled. This inclines more intelligent creatures to marshal resources, secure valued possessions, and man defensible positions (or get the heck out of Dodge). This can give the party time to recover from an initial encounter, to reassess the situation, and to prepare for danger.
This can also lead to concentrations of force away from incidental dangers (whether wandering or stationary), distributing the risk over time, and away from treasure valuable to the party but not the inhabitants. Goblins will generally not set up defenses around a library — even if they have discovered the wonder of toilet paper. The grandson of the village elder the party is sent to rescue may have fallen into a pit or been caught in a hunting trap rather than be held captive by dungeon residents or may use the diversion to attempt escape and so be found away from concentrations of defenders.
Creatures seeing the party as food would be an exception, but many of these would not rush in concert to possible food even if they are not ambush predators. Different creature types might have different territories and the strongest member of a group may get the first chance at tasty morsels with the others coming later to scavenge leftovers.
'Gik the Wimpy No Fight Tarks'
Fight is only one of the standard responses to a threat. Flight and freeze (hide) are other options that may be attractive to weaker or less invested creatures. It is not unreasonable for a young goblin to hide under his bed rather than fight alongside his skeleton friend (Nobody Likes a Goblin).
Undetected Activity
Partying Like It's the Last Day of Your Life
If a group of intelligent creatures are celebrating a successful raid or even just having a noisy coming of age ceremony, the noise of combat in moderately distant area might not be noticed. Even if guards are positioned to detect such a disturbance, they might be resentful of being excluded from the celebration and less attentive to their duties or less eager to raise an alarm ("You get Urg! I like my head attached.").
The Sound of Silence
If an intervening area has permanent magical silence, a guard might be placed just outside of the silent zone. This guard would only see the party when they enter the silent zone, so no rushed attack while the party handles its first encounter. If the guard attacks (after sounding the alarm) when the party is fully within the silent zone, the party may be able to defeat the guard before reinforcements arrive or choose to retreat and the guard decide to let the reinforcements pursue the party.
The locals could exploit this silent zone, particularly in attacking a spell-casting party. Alternatively, the locals might avoid the area because it is just too spooky.
The silence might have been set up to facilitate mediation by novice monks, to isolate a wizard's study/workshop, or just as a prank by some crazy wizard ("Bongzar the Inscrutable Was Here").
The Sound of Thundering Waters
Natural noise like waterfalls can mask combat even if nearby. More moderate noise might be annoying enough to the inhabitants that doors are kept closed; the clamor of combat mixed with moderate noise and muffled by a door may not be clear enough to draw a response.
Uncertain Activity
Was 'Alarm!' a Long Flat Trump or an Ascending Trump?
An inexperienced guard might use an 'All Clear' signal (close enough to the normal time) rather than 'Alarm!'. This implies that if the guard is defeated, a limited time would be available before the lack of 'All Clear' would raise an alarm. An individual might be sent to check on (and reprimand) the guard, but a wrong or unclear signal may not draw a strong urgent response.
We Know You're Out There, Somewhere
If the party is approaching from one of several paths connecting to a large echoing chamber, the reasonable response may be to gather a defensive force at that chamber rather than guess which direction to attack. Anyone hearing the combat may run back for reinforcements rather than try to determine where the party is.
The Orc That Cried 'Elf!'
If false alarms or drills have been common (or recent), the reaction to an alarm might be slow and half-hearted.
Ignored Activity
No One Escapes Shelob
If the initial encounter is with a formidable, commensal (not domesticated) guard creature, the "allied" denizens might not respond urgently to sounds of combat — they might even just laugh that they won't have to feed her for a few more days. A small scouting party — quite possibly the weakest, lowest status members of the group — might be sent to check on the result (and possibly gather any spoil) substantially later (while the intruders are being digested). Although the scouts would be cautious when approaching the area of danger, they would not be expecting the party and might be less cautious outside of the danger area.
If the greatest threat encountered in living memory was a lone hunter seeking shelter or a brown bear, the other occupants of the complex would not be expecting anything to survive. The adventurers might be tougher, more cautious, more prepared, or just luckier than the other denizens expect. Even level 1 adventurers are pretty formidable compared to a single commoner or a wild animal.
Remnants from previous meals might indicate the proximity (but not close proximity) of other, intelligent occupants. Humanoid bones without tools or clothing or bones with butchering marks could indicate a fed guard monster. Remains from unfortunate intruders may provide equipment. An adventurer's remains might give (potentially out-of-date) information about what threats the adventurer was expecting.
Somebody Else's Business
A fellow resident of an area may not be an ally. Fleeing or hiding and letting the others deal with the incoming threat is reasonable behavior for weaker creatures (even if their cooperation could have tipped the balance). Letting the mooks handle the intruders is reasonable behavior for a stronger creature or group of creatures.
Bound By Duty
A guard might be ordered not to leave his post. While the guard would sound the alarm when a threat is recognized (e.g., the sound of nearby combat), the guard might be much closer to the threat than to reinforcements. By the time reinforcements arrive, the party may well have completed the earlier combat and had time to evaluate their condition.
Similarly, a guard — who may be one of the more powerful combatants in a group — may not be sent to deal with an ordinary intrusion. The object of the guard's duty might be considered more important than avoiding a few combat losses, especially if the attack might be a feint.
Encouraging Forethought
Encourage the players/party to think about how to avoid having to fight every creature in the place at once.
Leaving Behind Special Gifts
If the party places distractions (spoil/food) or hazards behind it, a flanking response may be delayed, divided, or weakened.
- Some gaudy trinkets or fresh meat may distract creatures seeking to attack the party from behind. The creatures might be split between those rushing to attack and those getting the goods, contend over the spoil, or be delayed by having to enforce order.
- Caltrops in the direct path would typically slow (and weaken) a flanking group but do little to hinder the party's flight as they would know to go around the danger.
- A steepish slope presents an opportunity for greater delay. Oil or cave slime may be applied to make it slippery. Ball bearings at the top may lead to a pile-up if a creature falls down on ascending comrades. With orc-like personalities, this could lead to significant delay and potentially even a reduction in fighting strength. Since the party would be aware of the danger, their flight might not be slowed much (sliding down the slope might be faster than a normal careful descent).
Who Cares Who Brought the Beer, Let's Party
If the party earlier found a cache of nearly undrinkable (to humans) rum, they might think to leave a broken-down cart with barrels of rum on an ill-used path near the lair of goblins. Attacking while most of the goblins are drunk or hung-over is likely not only to delay or avoid sounding an alarm but also to make the response much more staggered. Drunk or hung-over opponents also act less intelligently, fight less effectively, and are less inclined to pursue aggressively.
This is just one example of the DM providing opportunities through ordinary low value resources ("Oh, what I wouldn't give for a holocaust cloak!") to make difficult challenges easier or more survivable. While the DM should not try to railroad the party into a specific plan (and not all players like strategizing or have a party that can be roleplayed that way), making resources available and even hinting at a possible uses (Player: "I dip a finger into the barrel and taste the contents." DM: "The barrel contains a rum so bad only an orc would drink it.") increases the odds of success or survival.
I Know Where You Live
If the party researches or scouts the area, the approach taken can account for possible cooperation and possibly even exploit conflict, hazards, bottlenecks, and timing of activity.
Part of this will often be simply part of the motivation for the adventure or rumors about the area. If more inhabitants/dangers are expected than can be handled at once, the party should be expected to be prepared for retreat and to use unusual means to limit coordinated responses.
E.g., knowing that wolves are one of the threats, the party might decide to approach in the later afternoon and enter in the early night when the wolves could be expected to be out hunting. Wolves remaining in the den will not be likely to leave the den to attack the party but will alert the other inhabitants (and the party).
If one likely opponent is too fast to run from, avoiding (going around, blocking, or distracting) or prioritizing (fighting while freshest) that opponent may be good tactics.
Even discoveries made while exploring can provide information about occupants and their interactions well before alerting them to the party's presence. E.g., a goblin skeleton at the head of one passage out of a chamber might tell the party that something down that passage does not want to be bothered by goblins and that goblins are probably elsewhere in the area.
Failure Is an Option
The party should be aware that becoming goblin poop is even less heroic than running away.
Noises like wolves howling or the sounding of a gong may give the party sufficient warning that they need to decide whether to retreat, use precious resources to finish an encounter more quickly, or prepare to face additional opponents while still dealing with the current opponent.
Planning for retreat can include disabling rather than moving around traps (playing hopscotch to avoid dart traps while fleeing the goblin horde is not wise, though putting a plank — that can be quickly moved off — over the triggers may be clever), having the means to slow pursuit (caltrops and ball bearings are somewhat affordable and light), marking the way to the exit (avoiding wrong turns or having to think about which way to go, though this can also alert patrols to the party's presence).
I Don't Know, I Just Live Here
Residents of an area are not necessarily familiar with all the paths through it. If the party discovers a secret or less observable passage, such might be used to hide from pursuit after a nearly exhausting encounter with the sound of reinforcements approaching. A party that explores — rather than hurrying from one combat to another — may find resources helpful later in the adventure.
Dynamically Adjusting Difficulty
Even if the party previously scouted the area and took a head count, adding or removing creatures is not necessarily unrealistic. The return of a raiding party or the visiting of a potential ally could add to the count; the opposite could reduce the count. The condition of the creatures can also be adjusted; sick or drunk/hung-over creatures are less capable and less likely to flee or act intelligently. Communicable illnesses might be a double-edged sword, helping the party succeed but keeping the party from returning immediately to civilization.
The usefulness of spoils can be adjusted dynamically. E.g., an unidentified potion can be mere treasure or a critical resource. Quaffing a believed safe but unknown effect potion can be used to give the party a chance to survive or escape an encounter without enabling the party to curbstomp their opponents. Using the potion to buff a character during a normal encounter might result in a useless effect (fire resistance might not be very useful against an ogre with a club), but used in desperation the potion might give just enough help to make survival likely.
Avoiding single entrance designs can facilitate escape (of residents or the party), allow the party to come from an unexpected or uncommon direction (initial disturbances might not even be recognized as signs of intruders), and provide an unexpected path for reinforcements (if the party is having too easy a time). This can also help to distribute dangers (both mobile and stationary) to reduce the risk of all the threats appearing at once.
Conclusion
Some of the above (particularly in "Undetected Activity" and "Uncertain Activity") should not be normal features of play but may not break the suspension of disbelief if used sparingly and sensibly (and perhaps with a little lampshading). Some of the above merely says that not all creature rush to attack intruders even if allies are in danger or an immediate pack response would be more effective.
Access to information (particularly sensory warning about coming danger and indications of the degree and type of dangers) can greatly help the party make good decisions about handling risk. In-dungeon resources such as defensible positions, places to hide, easily obstructed paths, useful equipment, and information about the nature and location of dangers can make a challenging task more survivable.
Restriction of information can allow the DM to dynamically adjust difficulty based on the circumstances. Mild, infrequent Deus Ex Machina coincidences like having the least encumbered and highest Dexterity member crossing the rope bridge when it breaks, having the dwarf hit by the poison dart, or having a falling block trap get stuck (so only tall characters take moderate damage on a failing saving throw rather than characters being crushed beneath tons of granite) — these can alert the party to danger if they are not being sufficiently cautious or nerf accidental failures without removing the in-story danger. Having the party saved at the last moment by Alexander Smugbottom the Magnificent may be a fate almost as bad as death, especially if the tale is recounted in taverns for miles around; such may add flavor to future activity ("You're the schmucks Smugbottom had to save from an elderly kobold?!" or "You're also a victim of Smugbutt the Magnifable's lies?").
