Monster infighting

Monster infighting is a term popularized by the FPS games in the "Doom" series and other similar games released in the 1990s. It occurs when two or more of the computer controlled opponents accidentally attack each other and then retaliate, causing a string of back-and-forth reprisals (hence, infighting). This can be accomplished most easily by moving the player character so that he is temporarily colinear with two adversaries; in the attempt to fire upon the player, enemies will cast their attack regardless of the fact a fellow monster may be within their line of fire either in front of or behind their intended target, thus subjecting their companion to friendly fire. The character hit by mistake will often become hostile and retaliate upon its attacker (often accidentally hitting other bystanders, especially with slow-moving and/or splash-damage attacks, leading to a vicious circle), thus starting the monster infighting.

This benefits the player in three ways: by reducing the number of enemies attempting to attack the player, by allowing the player to conserve ammunition, and by providing general amusement to players. Monster infighting has become a novel aspect of "Doom", its sequels, add-ons, and spin-offs. Indeed, many newer games do not give the enemies the ability to hurt each other, much less the ability to retaliate. In more recent first-person shooters, however, enemies are usually disciplined enough not to retaliate if they receive friendly fire.

Monster infighting in the "Doom" series

Some levels of "Doom" and "Doom II" sport large, open areas where a lot of monsters of different types are located; these levels are perfect for luring monsters into infights, and a few even revolve partially around making the monsters fight each other, as the player would stand little chance of taking out all enemies by himself. Examples of levels where this strategy can be employed are "The Courtyard", MAP18 in "Doom II", and "Gotcha!", MAP20 in "Doom II". In the latter of these, the player has to face the two most powerful enemies in the game at the same time, a Cyberdemon and a Spider Mastermind: the player can enhance his chances of survival by employing monster infighting, to let the two bosses shoot each other and eventually finish off the already wounded survivor.

According to "Doom" logic, however, monsters of the same type or species are immune to each other's projectiles, with the notable exception of firearms that use bullets, such as those used by the zombies. This means that getting two of the same monster to fight each other is very difficult, requiring a player to cause indirect damage by a nukage barrel explosion to the other. In version 1.1 of "Doom", a monster that had caused itself damage by destroying a nearby barrel would commit suicide, although this is actually a [ quirk in the game's infighting logic] .

A Lost Soul is an exception to the general rules of infighting due to its "charging" method of attack; if it charges into another Lost Soul, the injured Soul will retaliate once. If hit, the first Soul will then retaliate back, and so on, until one misses (at which point the Souls will resume attacking the player) or dies. Lost Souls will fight to the death any other class of monster that attacks it as usual.

Interestingly, Spider Masterminds who shoot bullets will also engage in combat with one another if hit. However, being a boss monster, it is extremely rare to find two Spider Masterminds so close to one another that would allow them to fight. In the original levels of the "Doom" series, the only such place is in "The Spirit World", MAP28 of "Doom II", and then only on the highest skill levels. In the Playstation port of Doom 2 the final level, "Icon Of Sin", was replaced (most likely due to the lower processing speed of the Playstation) with a new level called "Redemption Denied", in which two Spider Masterminds served as the game's final bosses. Due to the large arena they would invariably fight each other, and indeed the speech at the end of the game ("By turning the evil of the horrors of Hell in upon itself, you have destroyed the power of the demons") seems to refer to this.

The secret level of Final Doom Chapter 2, has many enemies, including 13 cyberdemons, which can easily be tricked into attacking one another.

Note that the game logic that renders monsters immune to their own projectiles is controlled by a simple flag in the executable file and can be toggled on or off by "DeHackEd" or similar executable-editing tools.

Monster infighting in the "Quake" series

Besides "Doom", it should be noted that similar monster infighting occurs in both "Quake" and "Quake II". The "Quake" manual even mentions that "some monsters hate each other even more than they hate you", and that the enormous Shambler creature is even feared by "other monsters". In "Quake II", more powerful enemies such as the hulking Tanks can be tricked into eliminating scores of weaker enemies.

Quake and Quake II are similar to Doom. Unlike Doom, however, the monster who was initially attacking the player "will" return to stalking the player after having won an infighting bout with another monster. AI is also improved significantly such that most enemies will get a clear line of fire before starting their attack; though when they are firing and tracking the player, the player can lead their projectiles to another monster.

Monster infighting in other games

Monster infighting is also present in many other game titles, occasionally as an obvious feature.

Billy Hatcher and The Giant Egg

In Billy Hatcher and the Giant Egg when you are fighting two or more dinosaur crows you can get them to attack each other, accidentally or on purpose. To do it on purpose, you have to get one to spot you, then run to, or be standing in front of another one. When the one that spotted you, charges [slides forwards on its belly, not its little runaround charge] run out of the way, which will cause the charging dinosaur crow to smash into the other. Also if you are in a small area/place, then when they try to attack you, (if there are more than two), they will all hurt each other in the process of charging and running.


In BioShock, the "Enrage" plasmid instantly causes monster infighting when thrown at one or more enemy targets in a group. Mechanical drones that normally target the player can also be "hacked" to attack each other instead.

Deus Ex

Deus Ex has three types of alliances: friendly, neutral or hostile, and each of these can be either permanent or not permanent. If an NPC A whose alliance with NPC B is neutral or friendly and not permanent is hit by B's bullet, or A sees B attacking A's allies, A attacks B. (There isn't any way to make an enemy friendly, though.)

For example, in Level 8, there are 6 riot cops and 10 UNATCO troops. After JC talks to Dowd, 10 MJ12 troops appear. These are three teams that are hostile to both the player and Dowd. Dowd is unarmed, but he is immortal. Make all three teams attack Dowd, and retreat to a safe location, such as the hospital. It will take the enemies seconds to take hits from other teams and start infighting. Those that don't die fighting their newfound enemies will eventually be killed by their teammates' stray bullets.

Other examples, excluding cases where NPCs start out hating each other:

*Paul and UNATCO in Level 1 (also, strangely, Paul only attacks the NSF if he sees them attacking his allies)
*Jonny (the pimp), UNATCO, and riot cops in Level 2;
*Luminous Path and military police in Level 6 Wan Chai market;
*MJ12 troops and MIBs in Level 6 VersaLife labs;

Fur Fighters

In the cult-classic third person shooter Fur Fighters for the Sega Dreamcast, ammo can be saved in many places by drawing fire from enemies and circle strafing in order to get them to fight amongst themselves. This is listed in the game's manual as a smart method of play.

Grand Theft Auto Series

Though not an FPS game, the GTA series contains instances similar to Monster infighting:

GTA 2 to GTA Vice City: Members of different gangs will attack each other on sight. Also, if the player is wanted by the police or a rival gang, he can hide behind any gang that isn't his enemy, and with enough luck, the police or rival gang will shoot the gang members instead of the player, sparking a shoot-out between your erstwhile enemies and the gang.

GTA 2 also features muggers. If a mugger tries to mug a gang member, other members of the gang will try to retaliate by shooting the mugger.

GTA San Andreas: Members of different gangs will attack each other on sight. Police NPCs will pursue and attack other NPCs committing an infraction (usually ramming police cars), or attacking the player.

Guild Wars

In Guild Wars, each monster belongs to an "army". Monsters in the same army will never fight each other, however monsters from different armies will at times (even without player intervention). Guild Wars also features a unique form monster infighting that is design intentional, and beneficial to the monsters. Minotaurs in the Crystal Desert will attack each other physically when no player is near. Dealing only minor damage to the monsters this behavior allows them to build "adrenaline" so when they engage the player their warrior skills are charged and ready for use at the beginning of the fight. This is, theoretically, an example of males in a pack jockeying for position in the groups hierarchy.


In Heretic (built on the "Doom" engine), the flying red gargoyles will fight each other if hit by fireballs coming from their own species and if the player is far enough not to distract them. If he approaches, they will turn on him instead. Also if the player dies the monsters in Heretic will start fighting each other


In the Marathon Trilogy, all monsters are flagged in relation to each other as "Friend," "Neutral," or "Enemy." Monsters that receive friendly fire from another monster they are "Neutral" toward will immediately begin to return fire (for example, S'pht Compilers will immediately counterattack "any" monster, except S’pht’Kr Defenders and other Compilers). Monsters that are enemies are equally willing to fight each other as they are the player, depending on who attacked the monster last. Monsters that are friendly to each other will excuse friendly fire.

However, certain monsters, when they are almost out of health, become "berserk" and, among other augmentations such as more speed and aggression, will attack "any" monster they see, regardless of their relation status. Because some of the berserkable monsters are fairly powerful enemies, this form of monster infighting is very useful, especially on the higher difficulty levels.

One point that makes monster infighting much easier to cause in the Marathon games is that Marathon's monsters almost all fire slow-moving missiles which allow more time for the player to move out of the way.

Peter Jackson's King Kong: The Official Game of the Movie

In the 2nd level, the game makes it clear that all the carnivorous species eat each other. Monster infighting occurs if one enemy is badly injured or if creatures are unaware of the player's presence. In this case, animals will devour each other. Besides normal monster infighting, the player can use harmless animals as bait.


Non-player characters in "Postal²" frequently engage in monster infighting, though they do not need to be hit by friendly fire in order to do so. In some instances, if a law-enforcement NPC comes into line-of-sight of any other NPC (or the player) brandishing a weapon, the police officer or Soldier will attack. The sound of a weapon being fired will also attract NPCs. As the game progresses, the gameplay world becomes more violent and NPC characters may be seen to spontaneously attack each other. As with "Doom", infighting-related encounters are not resolved until either the target, or the NPC attacking, have been killed. Even if the two NPCs lose sight of each other, they usually begin fighting again when they come back in view.

ilent Hill 1

There are several instances in Alchemilla General Hospital where the player can trigger the Puppet Nurses to attack one another. If the player runs between two nurses the enemies will reach out to attack the player, but will miss and end up choking one another instead.

pyro the Dragon Series

Enemies in the "Spyro" series can be tricked into attacking each other. Examples include gun monsters that fire upon worse armed enemies, and gnorcs that smash wizards with their clubs.

Turok Series

Monster infighting also appears in numerous Turok games. The player can stand in between two or more enemies causing them to either shoot from long range or attack up close. The player can then jump or sidestep out of the way causing an enemy attack to miss and strike another enemy thus causing the victim to retaliate. If the victim's attack connects with the attacker, infighting begins. The surviving "victor" will then retarget the player again and fight as normal. Only two or more enemies of different species can engage in infighting, never with their own kind, until 2008's Turok was released, where monster infighted was encouraged with the flare of the Shotgun allowing Dinosaurs of Different (Or even the same) species to fight each other or the players Human Enemies.

Resident Evil 3: Nemesis

If any zombies are close by to the character when the 'Nemesis' enemy also attempts to attack the character the Nemesis will often hit the zombies instead of the character (particularly noticeable on the Mercenaries subgame).

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