Immersive Citizens - AI Overhaul (Lite Version) is a plugin for "The Elder Scrolls V : Skyrim" whose purpose is to increase player in-game immersion by greatly improving Artificial Intelligence (AI) of friendly NPCs (citizens) in order to make them act and react like true humans in relation to their environment or to an aggressor. Specifically, this plugin deeply overhauls the AI used by NPC citizens when they are in a “standard state” and in a “combat state”. The “alert state” is left untouched. To explain, an NPC is in a “standard state” when he/she is unaware of an aggressor, a “combat state” when he/she has detected an aggressor, and an “alert state” when he/she is aware of an aggressor that cannot be located.
Immersive Citizens is officially featured by Bethesda Game Studios (source), therefore it has been tested and validated by BGS's quality assurance teams.

Combat State

Survival Instinct

Survival Instinct is a feature which gives nearly all the friendly and unique NPCs of Skyrim the ability to properly evaluate danger from an aggressor and respond to it more realistically while under attack. In short, if an NPC is attacked and has no chance of winning against an aggressor, that NPC will run away from the aggressor and attempt to find a safe place (a hideout). The hideout is chosen randomly, and the number of hideouts NPCs can access depends on the size of the city in which they live. Hideouts can be an NPC's home, the local temple, the Jarl's stronghold, a mine, the local barrack, etc. This Video will show this feature in action and will explain how it works. A more complete explanation is available below.

How it works: Basic Rules

• If an NPC is attacked by an aggressor who is 10 levels or more above them, the NPC will flee.
• If the attacked NPC's health is lower than a threshold percentage of that NPC's maximum health, that NPC will flee from the aggressor. At the moment, there are four percentage thresholds: 50, 40, 30 and 25. These thresholds are assigned according to the NPC's resistance to physical damages. For example, an NPC wearing a cloth outfit will flee once his health goes under 50%, while an NPC wearing full heavy armor and a shield will only flee once his health dips below 25%.

1. the NPC's current level
2. the aggressor's current level
3. the NPC's current health
4. the NPC's current resistance to physical damage (armor & armor spells)

• NPC(s) WILL NOT use Survival Instinct when they are currently enlisted as followers.
• Survival Instinct will only be used by friendly and unique NPCs.
• NPCs will use Survival Instinct against aggressors added by other plugins (Skyrim Immersive Creatures, Elemental Dragons, etc.).
• NPCs will use Survival Instinct against the player character (PC).
• Friendly NPCs added by other plugins (3DNPC, Inconsequential NPCs, etc) will also use Survival Instinct.

How it works: Advanced Rules

In addition to the rules cited above, special rules have been assigned to several NPCs (but not all) according to their personalities and their social rank. These rules have priority over the general rules when they conflict.

Civilian NPCs: The NPCs within the "Civilian" category never try to counter the aggressor when attacked. If they are attacked, they will flee and try to alert the guards. An NPC falls into the Civilian category when meeting ALL of the following requirements:

• The NPC's maximum level is capped at 10 or less.
• The NPC is unarmored
• The NPC is unarmed (EXCEPTION: a dagger alone doesn't count as 'arms')

Strategist NPCs: The NPCs categorized as "Strategist" will tactically retreat for a few seconds once their health is reduced by half. During this move, they will keep their distance while healing themselves and refreshing their protective spells. Once finished, the Strategist NPC will go back into the fight. An NPC falls in this category when meeting ALL of the following requirements:

• The NPC is a member of the College of Winterhold
• The NPC has a mana pool higher than 63

Cautious NPCs: The NPCs categorized as "Cautious" will flee any aggressor who is more than 5 levels higher than them (instead of 10). Furthermore, these NPCs will flee when attacked by an "impressive" aggressor, even if the NPC is a higher level. Specifically, the following creatures are listed as being impressive: dragon, giant, giant spider and mammoth. An NPC is considered cautious when meeting ANY ONE of the following requirements:

• The NPC is a member of the Thieves Guild
• The NPC is a member of the Dark Brotherhood
• The NPC wears a cloth outfit (or is naked) and has no knowledge of protective spells

Fearless NPCs: The NPCs falling in the "Fearless" category fight to the death, regardless of their aggressor's attributes relative to their own. An NPC is considered fearless when meeting ANY ONE of the following requirements:

• The NPC is under the influence of a frenzy spell
• The NPC is dead (reanimated NPCs will fight until they turn to ash)
• The NPC is a member of the inner circle of the Companions

Khajiit Merchant NPCs: Unlike the other NPCs of Skyrim, Khajiit merchants will stay outside cities when they decide to flee. If they are near a city, they will hide inside a guard tower (Solitude, Riften), inside a city wall (Whiterun, Markarth, Windhelm), or inside a mine (Dawnstar). If they decide to flee while traveling between cities, they will flee in the direction of their destination.

Sleeping Agent NPCs: The vampires and Forsworn who hide among the NPCs of Skyrim will act as civilians unless they are attacked by the Dragonborn or if the time has come for them to show their true nature.

Combat Styles

Warrior NPCs

NPCs assigned to the "Warrior" class rely upon counter attacks to survive. For example, most Warrior NPCs will bash their aggressors (with high probability of success) when an aggressor tries to perform a power attack or a rapid succession of regular attacks against the Warrior NPC. Once the aggressor is staggered, the Warrior NPC will only perform one or two regular attacks while the aggressor doesn't have time to block.

Mages & Thieves/Archers

Standard State

Weather Influence

• Pleasant
• Cloudy (foggy weathers also fall in this category)
• Rainy
• Snowy (sandstorms also fall in this category)

The citizens will adapt their activities according to these weather categories. During snowy or rainy weather, NPCs will stop their outdoor activities and will go back to their homes if they are outdoor.
If they go back to home between 8am and 8pm, the NPCs will open their doors once inside their home (assuming they have one). However, if a NPC enters in its house while the player is already inside, NPC will ask the player to leave and will lock the door until the next day. If an NPC does not have a home, he/she will take shelter inside a tavern or in another public area. If there is no public area around, he/she will look for a fire camp. Note that NPCs will not use this feature if they are riding a horse or if they have one of the following jobs:

• Miner
• Lumberjack
• Blacksmith
• Ferryman
• Carrier

Miscellaneous

In game configuration menu

Immersive Citizens comes along with an in-game configuration menu allowing you to reboot, disable or update properly Immersive Citizens on your save. It also allows you to turn off some features that you may dislike. To have access to the MCM menu, SKSE 1.6.9+ and SkyUI 3.2+ are required, but they are NOT required to ensure the mod functionality, therefore they are optional.

This plugin only affects the NPCs which are friendly and unique (named). Exception: The AI used by some guards in Whiterun has been improved. In total, Immersive Citizens improves the behavior of 601 NPCs.

Official NPCs

At this time, Immersive Citizens improves the AI used by NPCs living in the zones shown below and highlighted in green. The color code shows features implemented for each area.
Green: All features have been implemented.
Grey: No modifications.

Unofficial NPCs

If you use one or several plugins adding friendly and unique NPCs, "Survival Instinct" and "Go Home" will be implemented in these NPCs. Note that, like "Wet & Cold" or "Run for Your Lives", "Immersive Citizens" will only handle a limited number of additional NPCs, here are the limitations:

• For the additional NPCs assigned to vanilla city/town/settlement, the limitation is 50 extra NPCs per vanilla city/town/settlement.
• For the additional NPCs assigned to new city/town/settlement or living in the wild, the limitation is 100 extra NPCs per hold (region).
• If you install a mod on an old save which adds extra NPCs while "Immersive Citizens" is already active in this save, don't forget to update "Immersive Citizens" through the configuration menu (more information in the section: Installation, Update & Load Order).

Incompatible Plugins

In theory, the lite version is compatible with everything. The compatibility level of the lite version is the same than the mod "Wet and Cold" and is better than than the mod "Run for your lives".

Interaction with quests and with plugin modifying NPCs AI

The AI temporarily implemented by vanilla quests have a higher priority than the AI implemented by "Immersive Citizens". Therefore, "Immersive Citizens" doesn't prevent the vanilla quests to work as intended. Popular mods improving NPC AI such as Wet & Cold and Holidays implement also AI with a higher priority than the one added by "Immersive Citizens". It's not a problem because AI from these mods are only used under very specific conditions. To summarize, either my AI has priority or my AI is overridden. Here is a concrete example involving the following mods: Wet & Cold, Holidays, Sleeping Innkeepers, My Home Is Your Home (MHIYH), Enhanced Skyrim Factions: The Companions Guild and my plugin. Whatever your load order, the game engine will use the modifications done on the AI by these plugins according to this order of priority (from top to bottom):

1. Wet & Cold, conditions: The “Go Home” feature has been activated in the menu and it’s raining or snowing
2. Holidays, condition: Active only during specific dates
3. My Home Is Your Home, condition: Active only on followers selected through MHIYH's menu
4. Immersive Citizens – AI Overhaul, condition: none
5. Enhanced Skyrim Factions – The Companions Guild, condition: none
6. Sleeping Innkeepers, condition: none

In practice, this means that the game engine will never use the AI modifications done by the mod “Enhanced Skyrim Factions: The Companions Guild”, because I have already overhauled the AI of all members of the Companions, but it will still use all the other features from this mod. If you have “Wet & Cold” installed, the game engine will use my feature “weather influence” only if the “Go Home” feature from “Wet & Cold” is disabled.
Concerning "Run For Your Lives" & "When Vampires Attack", there is no interest in using them if you use Immersive Citizens, for the following reasons:

• Immersive Citizens supersedes these mods. Indeed, the feature "Survival Instinct" from Immersive Citizens works against any hostiles whatever the situation whereas "Run For Your Lives" & "When Vampires Attack" works only against some vampires and some dragons in very specific situations. Therefore, you won't get significant benefits in using them with Immersive Citizens, only downsides. For example, according to the author of "Run For Your Lives", sometimes "Run For Your Lives" can stuck forever NPCs inside their house, which is rather game breaking, more information about this issue can be found here. Due to the way immersive Citizens has been designed, NPCs can't get stuck forever in their homes which is a another major advantages of Immersive Citizens. This is why all the most popular mods compilations (STEP, Neovalen revisited, etc.) has definitely ditched "Run For Your Lives" & "When Vampires Attack" in favor of Immersive Citizens. Don't also forget that more mods in your load order also means potentially more bugs, more load order problems and more compatibility problems to deal with.
• If you're looking for an additional security, then any mod which adds a protected/essential flag to all NPCs (such as NPCs Protected Redux) will be much more efficient and complementary than "Run For Your Lives" & "When Vampires Attack". Indeed, although Immersive Citizens is very efficient to keep NPCs alive from agressors, sometimes, due to a game engine bug, some NPCs will die by falling either because they have been loaded too far away from the ground or because they have falled through a mesh. The only efficient way to protect NPCs against this kind of death is to use a mod which adds a protected/essential flag to all NPCs. It has been confirmed that this bug occurs without mods (source).
• Since the version 0.2.5, if you install on your save a mod adding extra NPCs while Immersive Citizens is already loaded in your save, then all you need to do to allow Immersive Citizens to affect these newly added NPCs is to update "Immersive Citizens" via a configuration menu available through a Power called "Citizens control" present in the magic section. Therefore, there is definitely no more interest to use "Run For Your Lives" & "When Vampires Attack" if you use Immersive Citizens.
• They may decrease your immersion. Indeed, NPCs will flee while there is no threat in sight, because these mods give to NPCs the ability to anticipate a dragon or a vampire attack, which is really something that ruin immersion in my opinion. This is why I ditched these mods and I started to develop my feature "Survival Instinct".

Concerning "Wet & Cold", unless you are only interested by the "Go Home" feature from "Wet & Cold", it is interesting to use it along Immersive Citizens. For your information, the “Go Home” feature from “Wet & Cold” is automatically disabled if you use Immersive Citizens. The author of "Wet & Cold" took this decision because the "Go Home" feature has been designed in a similar way than "Run For Your Lives" & "When Vampires Attack" and therefore it has the same bugs. Indeed, sometimes this feature can stuck forever NPCs inside their house.

Interaction with "Follower Overhauls" such as UFO, AFT & EFF

If you use UFO or EFF, your follower(s) won’t use “Survival Instinct”.
If you use AFT you have the possibility to turn on/off "Survival Instinct" for your follower(s). With AFT "Survival Instinct" is activated by default. To disable it or to reactivate it, talk to your follower(s), go in the tweak menu, then in the combat menu, choose a combat style to disable it or choose 'None' to reactivate it.

Interaction with plugins altering NPCs

Due to the way Immersive Citizens has been designed, Immersive Citizens is compatible with any plugins altering NPCs (inventory, outfit, appearance, faction, etc.).

Interaction with "Combat Overhauls" such as Requiem, Skyre, Smilodon & Ultimate Combat

Due to the way Immersive Citizens has been designed, Immersive Citizens is compatible with any combat overhauls. Immersive Citizens is the first and for now the only one to modify the root AI used by NPCs when they are in combat, therefore, if you use a mod which edits combat styles, friendly and unique NPCs will use my combat styles whatever your load order. There is no bad or good synergy with those mods.

Installation:
To install Immersive Citizens, it is recommended to use a file manager such as Nexus Mod Manager (recommended for newbie). If you use Nexus Mod Manager, click on the "Download NMM" button (located here) and follow the on-screen instructions. The custom installer will automatically select the required compatibility patches according to your plugin list. Then, ensure that the plugin(s) are activated.
For a manual install, download the file (the link can be found in the files tab of Immersive Citizens page), then extract in your Skyrim data directory (...SteamSteamAppscommonSkyrimdata) the content of one of the following folders: 11_Main_Lite_Version.

Update/Reboot:
To update Immersive Citizens on your install, uninstall the old version of Immersive Citizens then install the new one.
To reboot or to completely update Immersive Citizens on your save, you can use the MCM menu. Open the MCM menu dedicated to Immersive Citizens, then in the general tab, untick then tick all the boxes which was ticked when you opened the menu, afterwards close the MCM menu.

Does your AIs are scripted / script-intensives?
No, the AIs are not scripted. Immersive Citizens adds only 4 scripts. One of them runs only once (during around 1 second) and his purpose is to activate Immersive Citizens the first time that you load it in your game. Another one is used to ensure compatibility with weather mods and to update Immersive Citizens when you install a new version. The 2 last one allow to add in-game configuration menus and thus, they run only on player command. Before the version 0.2.5, the mod was script-free.

Does your plugin have a significant performance impact?
No, no significant performances impact (around 1%).

Can I expect a lot of bugs?
No, all the AI added by Immersive Citizens have been tested by myself. I didn't delegate this task to individuals unrelated to this project due to the fact that it would require that I publish and update regularly the 574 decision trees, which is a tremendous amount of work with no guarantee of results. Therefore, I took the decision to test all the decision trees by myself rather than to spend time publishing decision trees because this assures me guarantee results.

Do you plan to make a lite version for Skyrim SE?
Yes, but no ETA though. The original edition of the lite version is used by few individuals, therefore, it's not a priority.

Is there a way to prevent extra citizen from being affected by your mod?
Yes, I created a faction for that purpose: NPCO_ExclusionFaction.

How long will a hostile stay in front of a citizen's door?
Assuming you do not leave the area, this is determined by the following game setting: fCombatDetectionLostTimeLimit. This game setting has been set to 300 which is 5 minutes. By modifying this value, you can get results which are completely different. For example, with a value of 60, you will have citizens fleeing around you permanently during your fights. This will add a lot of chaos. Some will like it, some will not.

How long will a citizen remain in a combat state once he reached a hideout?
A citizen will not be in combat state anymore if you kill his foe or if X minutes have past where X is equal to the value set for fCombatDetectionLostTimeLimit.

Once a citizen is no longer in a combat state, how long it takes for him to leave his hideout?
With the default time scale, it takes him between 1 & 120 seconds. If you use a timescale of 10, it will takes between 2 & 240 seconds.

What time scale is safe to use?
The AI has been designed to use the default time scale (20). It will work with any values between 0 and 20 (I don't see the point to increase the value unless to perform tests); however, I do not recommend to go under 10 because beyond that there are boring downsides. For example, if you use a value of 10, the time between the dragon attacks is increased by 2, the conversations between the citizens will need twice the time to reset, the citizens will need twice the time to leave their house after an attack, etc. Moreover, a lot of quests or mods (such as "Holiday" from Isoku) use the in-game clock and may stop working as intended if you decrease the time scale too much, so choose wisely.

If a quest does not work as intended, it is very likely that the culprit is not Immersive Citizens because Immersive Citizens inject to NPCs an AI with a low priority. Most of time the culprit will be a mod injecting to NPCs an AI with a high priority or a mod belonging to one of the following category:

• Town Overhaul (Open Cities Skyrim included)
• Interior Overhaul
• Alternate Start

Game Engine Limitations

Fast Travel

The game engine is not able to update the position of NPCs during a fast travel. Therefore, if you fast travel directly to Whiterun, most of Whiterun's citizens will be late on their schedule. For example, if you arrive during night time in a city via the fast travel, you will find in the streets a lot of NPCs walking toward their house in order to sleep. If you arrive during day time, you might find several shops closed.
To bypass this game engine limitation, I use the fast travel to reach a location near the city where I want to go. For example, instead to fast traveling to Whiterun, you should fast traveling to a watchtower near Whiterun. Because it's a game engine limitation, you will have the same problem with the vanilla AI.

Sleep/Wait

The game engine is not able to update the position of NPCs which are not moving when you use the sleep or wait menu. Therefore, if you sleep in an Inn between 10 pm and 8 am, when you wake up, all NPCs who was sitting when you started to sleep will be still there.
To bypass this game engine limitation, if you want to sleep in a public area, I recommend to start to sleep around midnight. You can also use the wait menu or sleep menu twice in a row. For example, you can sleep 7 hours, wait 2 seconds in order to allow the NPCs to stand up and to start moving. Then sleep again 1 hour.

NPC & Door

Sometimes, an NPC can be interrupted when he is opening a door (linked to a teleporter). If an NPC opening a door is interrupted, then he will stay during several seconds in front of the door he tried to open and therefore he will block the path leading to this door. As a result several NPCs may stack temporary in front of this door.
Sometimes, NPCs are no more able to navigate from a room to another room. To fix this issue, reboot Skyrim.

Miscellaneous

My game crashes (CTD) before I reach the main menu.
Either you do not meet the requirements (you do not have Dragonborn or Hearthfires or Dawnguard or use a pirated version of Skyrim), or you have installed a compatibility patch that you do not need, or your plugin load order is incorrect. The custom installer will automatically select the required compatibility patches according to your plugin list, if a option is not ticked, then you don't need it. If you get a crash before to reach the main menu, I recommend first to reinstall Immersive Citizens by following the recommandation from the installer. If the problem persist, start TES5Edit, select all your plugins, and press OK. If a plugin is missing or if your load order is wrong, TES5Edit will give you a very explicit error message, as well as the name of the missing plugin or the name of the poorly sorted plugin.

I have a reproducible CTD in game when I try to update an old save.
If you have a CTD just after an update, reinstall the previous version and load your save, afterwards go in a nonpopulated area, disable Immersive Citizens by using the in-game configuration menu, then save. Once done, install the new version, load your save and reactivate Immersive Citizens by using the in-game configuration menu.

Most NPCs gather in some areas, then they stop to move and remain there for several hours or forever.
Most NPCs do not enter their home or do not leave their home.
NPCs are blocked by invisible walls.
This usually happens when you use mods which are not compatibles with Immersive Citizens or when you stack plugins which modify the layout of the same place(s) or if you load order is incorrect. This can also be caused by a single plugin editing navigation meshes. Keep in mind that any plugin which edits navmeshes can potentially disrupts the navigation of NPCs and thus can disrupt the AI used by NPCs. Hopefully it is reversible as soon as you remove the culprit.

• First, make sure that you have respected my recommendations about the load order.
• Then, ensure that you are not using a plugin listed as being incompatible (see this page).
• If the issue persists, remove the plugin(s) which edits the architecture of the area in which the issue occurs.

Vilkas complains that I am using magic during the quest "Take Up Arms".
NPCs attack me during a brawl.
This happens when you use an enchanted weapon or a mod that adds a hidden cloak spell on the player. The purpose of a cloack spell is to add new abilities to nearby NPCs through a scripted magic effect. When the cloak spell hits surrounding NPCs, they will think that magic is used against them or that you are attacking them. Lots of scripted mods can cause this. This mod should fix your problem.

My follower always runs away while I am fighting against a dragon.
You use a follower overhaul such as AFT. If you use AFT, you have the possibility to turn on/off "Survival Instinct" for your follower(s). With AFT, "Survival Instinct" is activated by default. To disable it or to reactivate it, talk to your follower(s), choose "let's talk about your abilities", then choose "change your combat style". Choose a combat style to disable "Survival Instinct" or choose 'None' to reactivate it.

NPCs stay permanently inside their home.
Citizens don't react when I attack them.
Not related to Immersive Citizens. "Run for Your Lives" and "When Vampires Attack" are known to cause sometimes this bug. More information about this issue can be found here.

A dialogue does not show up to start a brawl against an NPC or to start a secondary quest.
This kind of bug is usually caused by the use of an alternate start mod. Here are some examples of issues which have been copied from the description of "Alternate Start - Live Another Life" :

• The Thane offer won't be available in every city right away if you use a property owner start. The quest interaction makes doing so impossible without sacrificing too much of the content to it.
• When choosing one of the two civil war starts, you are strongly advised to let the Jagged Crown scene play out. If you don't, the quest may fail to start and the entire civil war quest line will get jammed.
• Some quests in a major city you pick a start for may not be available until after you've left that city and returned later. This is normal. It's due to how "Change Location" events work in the game and there's nothing that can be done about it.

The introduction scene (The Forsworn Conspiracy) in Markarth doesn't start.
This is not related to Immersive Citizens. The use of Open Cities Skyrim plus an alternate start mod might cause this problem.

After a fast travel, I found dead NPCs, however I don't know how they died.
It's very likely that they died by falling because they went through a mesh or because they have been loaded far away from the ground. It's a vanilla bug, presents since the release of the game. It has been confirmed by multiple individuals that this bug occurs without mods, click here to get an example. It seems that this bug occurs often when you use the fast travel system. Some NPCs seems to be specifically affected, such as eorlund (source: http://elderscrolls.wikia.com/wiki/Eorlund_Gray-Mane). The use of Open Cities Skyrim might also increase the frequency of this bug.

An NPC is late on his schedule.
Very likely because you have used the sleep menu or a the wait menu more than 1 hour or because you have done a fast travel. To fix this, open the wait menu and wait 1 hour.

Help ! I'm a newbie, I don't know how to install your mod.
If you are a beginner, first, I recommend you to watch this guide as well as this tutorial to learn how to clean your DLC.