The distinction between this section and the next two ("tactical challenges") is a bit arbitrary, but basically components in this section either don't alter creatures' abilities at all, or do so in a relatively low-key way.
This component has no in-game effect, but carries out some preprocessing that's necessary for any of the other AI/tactical components to function.
(For experts: it constructs a centralised list of which spells and items use opcode 206, builds lots of prebuff and instant-effect spells, and constructs the "cursed wound" item used by clay golems.)
Smarter general AI
This component improves the generic AI used in melee and ranged combat throughout BG2. In addition, it rearranges creatures' choices of proficiencies and (where appropriate) high-level (non-spellcaster) abilities, assigns kits to some fighters and thieves who don't currently have them, and ensures that creatures have correct (or at any rate consistent!) saving throws, attack rolls, levels, and kit abilities. It will mostly affect fighters, thieves, and monsters without large numbers of special abilities.
Main features of this component include:
Enemies will try to choose targets more intelligently. This will be most noticeable for ranged attackers - the game's engine makes it difficult to safely tell melee fighters to do much more than "attack nearest".
Melee attackers will fairly quickly notice that their opponent is immune to their attacks (if you're protected from magic weapons, for instance) and will try someone else; ranged attackers will similarly notice spells like Physical Mirror.
Thieves will use their backstab and hide-in-shadows power as much as they can, and will avoid wasting backstabs on characters with Stoneskin or Mirror Image.
Enemies will use potions if they have them (though this component doesn't give them any).
Enemies with class abilities (e.g. Kai) or high-level abilities (e.g. Whirlwind Attack) will use them.
Enemies above a certain minimum intelligence will usually prioritise opponents who are not stunned, held or otherwise helpless. From their point of view, they're fighting to win, and if they kill all non-helpless opponents they can finish off the helpless ones at their leisure. (They will, however, finish off nearby vulnerable opponents in preference to chasing up distant ones.)
In Baldur's Gate I, various creatures who foolishly moved up to talk to the party, or sat immobile while being surrounded, will now initiate conversation at a distance.
About a dozen (in BG1) or about seventy (in BG2) creatures now have kits assigned. Kits used are archer, assassin, barbarian, berserker, kensai, swashbuckler, and wizard slayer.
Better calls for help
This component substantially improves the (in BG1 almost nonexistent, in BG2 rudimentary) scripting for monsters to help one another. Even the stupidest monsters will fight in groups (so the advance-a-few-steps-at-a-time strategy will fail); intelligent monsters will call out to nearby allies. There are some ways to abuse this component but generally it seems to strike a good compromise between amazingly unrealistic behaviour on the one hand, and the entire map emptying towards you on the other.
High-Level Abilities for spellcasters (BG2,BG2EE,BGT)
This component allows high-level spellcasters in BG2 to use High-Level Abilities (HLAs). The component has no effect unless the Smarter Mages and/or Smarter Priests component is installed (really it's just a component choice for those components, not a component in itself). There are five options, allowing HLAs to be available for only special creatures, or all sufficiently-high-level spellcasters, in Shadows of Amn or Throne of Bhaal or both.
Warning: The option is available to let all Shadows of Amn spellcasters use HLAs, but this will make some early parts of the game extremely dangerous, and I don't really recommend it. If you ignore this warning and then get Dragon Breath dumped on your twelth-level party, don't blame me.
This component drastically improves the intelligence of pretty much all the arcane spellcasters (liches, mages, fighter/mages, thief/mages, bards) in the game. It does so in three ways:
Better choices of spells and sequencers. The spell lists of mages are systematically restructured to swap useless for useful spells. I've tended to err on the side of variety over usefulness: Maze is less useful than Horrid Wilting but it's still fairly useful, so I've kept it; but Larloch's Minor Drain just can't compete with Magic Missile, so out it goes. Enemy sequencers, spell triggers, contingencies and the like are all completely reworked. Both the spellswap and the sequencer choice are done at random (though occasionally I've tweaked it for specific mages) - I think an 18th level wizard has about 4000 different possible combinations of contingencies and sequencers! Spell choices will change each time you reinstall SCS ; sequencer and contingency choices will change each time you reload.
(Whether mages use High-Level Abilities will depend on whether you installed the appropriate component above.)
Much better targeting. SCS mages are very, very careful to choose sensible targets for their spells and to avoid silly or unrealistic actions. They will renew magic defences as soon as they are destroyed, try to show some discernment in when to use antimagic attacks, prefer to target fighters with Dire Charm and mages with Power Word: Kill, etc. Multi-class characters will try to intersperse their mage and non-mage abilities. There is quite a lot of randomness, though - partly because it's tactically unwise to use too-fixed a strategy, but mostly for variety.
SCS tries extremely hard not to cheat. It's impossible within the engine to be completely certain of this, but as far as I can manage, no SCS mage does anything that the party can't (assuming that you have installed the Spell Tweaks components of SCS ). There are two exceptions:
As noted in the "Improved Fiends" component (below), if you install that component then NPC-summoned fiends behave a little differently from PC-summoned ones.
I assume that NPC wizards (who have years and decades more practice than the PC) can specify the conditions on which their contingencies go off with more discernment than the PC, so I haven't restricted myself to the conditions that the game allows for PC spellcasters. Otherwise, I have kept to the standard Contingency rules even when the unmodded game breaks them (no choosing different targets in the same sequencer; no 9th level spells in Chain Contingency, etc.)
SCS mages obey the rules on invisibility: only spells which can be cast at a point on the ground can be used against improved-invisible opponents. So they will cast Horrid Wilting or Fireball at your improved-invisible character, but not Breach or Magic Missile. One unavoidable game-engine, glitch, though, is that (unlike with PC spells) an NPC-cast Fireball will land at the feet of its target even if s/he has moved after casting began. I can't do much about this. Note that sequencers cannot be, and are not, targetted at invisible opponents (even if they contain area-effect spells); but note also that liches can see through invisibility (even in the unmodded game).
Out of mercy, enemy mages won't cast Imprisonment on the main character. If you're masochistic enough to want to change this, enter CLUAConsole:SetGlobal("DMWWImprisonPlayer","GLOBAL",1).
SCS allows mages to cast some spells instantly, to simulate casting before battle begins (in BG2 it's very difficult to script enemies to do the sort of pre-battle buffing that PCs can do). They will always do this with any spell with a duration of more than a couple of hours (e.g. Stoneskin, Melf's Minute Meteors). There are five options, though, for the casting of short duration spells. (Note that whichever option you choose, mages will still use contingencies and spell sequencers.)
Option 1: Mages are always allowed to cast spells instantly at the start of combat. This is basically the same way magic works in SCS, and is tactically the hardest challenge; however, on occasion it might appear a bit unrealistic.
Option 2: Mages are allowed to cast spells instantly at the start of combat only when they are created near the PC (e.g. enemy mages teleporting in to ambush you). This is basically how Tactics handles this (though I think I keep to the rules more strictly than Tactics does). It's somewhat less challenging, but since even casters whom you catch off-guard have contingencies and sequencers to defend themselves with, mages can slam up defences pretty quickly.
Option 3: Mages never cast spells instantly. (Though, again, they can very quickly use contingencies and sequencers to defend themselves.)
Option 4: Option 1 for BG1, option 2 for BG2. The logic here is that many mages in BG2 teleport in, but hardly any do in BG1 - partly because they are lower level, partly because of different design philosophies. (For what it's worth, this is my own preferred option.)
Option 5: Mages use short-duration spells at the start of combat, but only if the difficulty is set to Hard or Insane.
This component also makes some systematic adjustments in the levels of NPCs. The unmodded game is very inconsistent: it often makes casters much too-low-level for the spells they have (this matters because many spells have different effects at different levels, and also because Dispel Magic depends on the difference in levels between the casters. SCS goes through every arcane caster in the game and modifies their level according to the following rule: an NPC is raised to the lowest level consistent with all the spells s/he knows, except that no-one is raised to a level that would let them cast higher-level spells than they actually have, and (almost) no-one has their level reduced by SCS II. This is then fine-tuned manually.
Finally, many wizards will be specialists of one sort or another (I use necromancers, conjurers, invokers and enchanters), and this should - hopefully - lead to a little more variety in the kind of spell use you see.
The component uses whatever memorization rules are in the game. If you've installed a component which changes the number of spells a caster of a given level can learn, this will apply to enemy mages too; if you've opted for High-Level Abilities to work as innate abilities rather than spells, this is how mages will use them.
Since Irenicus is a mage, this component upgrades him too. He gains no new spells, but he should use his existing spells more effectively, and this makes him a lot more dangerous (particularly in his final incarnation). Illasera is a fighter-mage in the unmodded (non-Ascension) game, so if you don't install Ascension then she gets upgraded. If you have the "Smarter Clerics" component then Sendai is also upgraded (unless you've installed "Tougher Sendai" from the Oversight mod).
This component upgrades the intelligence of the clerics and fighter-clerics in the game, in much the same way as the "Smarter Mages" component does for mages etc. It has the same three pre-casting options; note, though, that since clerics do not have access to sequencers or contingencies, enemy clerics are at a huge disadvantage on options 2-5. (For this reason, my own preference is to use option 1 for clerics.)
Potions for NPCs
Potions are one of the most effective and cheap ways for a humanoid creature to enhance its combat ability. The party collect literally hundreds of them through the game and can easily buy hundreds more; it's not that realistic that enemy NPCs don't have them. This component gives healing and protection potions of various sorts to humanoid NPCs; it also gives combat-boosting potions to fighters and invisibility potions to thieves. The potion allocation is based on level (the higher level your opponent, the more likely he is to have good potions); it also requires a higher level for a Throne of Bhaal NPC to have potions than for a Shadows of Amn one, since Throne of Bhaal is crawling with mid-level grunts, and a higher level for a Shadows of Amn NPC than for a BG1 one.
This component "plays fair", in the sense that potions are given to NPCs when they are created, not beamed into existence just in time to be drunk. This means you'll probably end up with (even) more potions if you use this component, since you'll be able to steal a few from enemies who are killed before being able to use them. However (as Alesia_BH pointed out to me on the Bioware boards) it's not exactly unrealistic that glass bottles get smashed in the heat of battle. So you can choose any of six different rules for what fraction of potions are recoverable.
The Superior Healing potion only gets given to enemies in Throne of Bhaal (to preserve a flavour difference between the two components).
This component enhances the AI (and in some cases, the abilities) of most of the spiders you meet in the game. Its effects will be most noticeable in BG1 - it makes the Cloakwood, in particular, quite challenging. Basically, there are two main changes: giant spiders cast (single-target) webs every few rounds, and phase spiders teleport more effectively. All spiders also have an increased predisposition to attack webbed opponents and poison them.
Smarter dryads and sirines (TUTU/BGT/BGEE)
This component improves the intelligence of sirines - their charms will be better targetted and they make more intelligent use of their invisibility. It also adds a little defensive magic to the hamadryad of the cloakwood - she is hopefully a little more of a challenge now.
Slightly smarter carrion crawlers (TUTU/BGT/BGEE)
This small component gives carrion crawlers a slightly smarter script - they know enough to continue paralysing moving opponents before feeding.
Smarter basilisks (TUTU/BGT/BGEE)
This component spreads basilisks' gaze attacks around, rather than mechanically petrifying the nearest target. More importantly, it gives them the intelligence to see (eventually) that some targets are immune altogether, and to concentrate on others.
Improved Golems (BG2,BG2EE,BGT)
This component doesn't really make golems smarter (they're supposed to be stupid) But it streamlines their scripts a bit, gives their weapons a sensible range, makes them immune to Lower Resistance and to poison, and tries to prevent situations where golems get stuck behind barricades. It also fixes an animation glitch in the Iron Golem animation - this hopefully makes iron golems a bit prettier when they attack and blow clouds. As of version 22, it also gives clay golems a cursed-wound weapon, as in PnP Dungeons & Dragons. (You can turn this off before installing - see the Customisation section.)
Improved Fiends (BG2,BG2EE,BGT)
This component overhauls the "Fiends" (i.e., Baatezu and Tanar'ri, aka Devils and Demons) throughout SoA and ToB. More than any other component of SCS II, this component not only upgrades their scripting but actually gives them a variety of new magical abilities. I've based the abilities the fiends received on a combination of 2nd and 3rd edition pen-and-paper D&D; details can be found in the Spoilers section. However, the fiends' basic combat abilities and defences remain essentially unchanged: other than a certain amount of systemisation (where two similar-looking fiends have wildly different immunities, for instance) I've left their hit rolls, damage, immunities, magic resistance etc pretty much alone. In fact, in one or two cases I've removed a power (e.g. permanent haste) that seemed to be added as a cheesy way of making a fight harder.
The component also enforces the fact that fiendly spellcasting is instantaneous and innate, so that fiends do not use up time getting their spells off, and cannot be interrupted.
This component also makes a substantial change to the way fiend-summoning magic works (this is one of the few places where SCS II breaks the rule that players and NPCs should be treated equally). I assume that enemy spellcasters (who, after all, have been learning high-level magic far longer than the party) summon demons with whom they have a pre-existing pact. These demons won't attack their summoner - and, crucially, will attack the party even if they are protected by Protection from Evil. The practical upshot is that the only demons in the game now kept at bay by a Pro/Evil are the ones that your party summons. This makes summoned demons rather more useful, and you'll see more of them being summoned. Note: this component will only have an effect on the game if you also install SCS 's "Smarter Mages" and/or "Smarter Priests" components; unmodded priests and mages continue to use the original version.
The component also offers the option to increase fiends' hit points by about 50 percent. (In playtesting, I found that this led to more interesting battles, with fiends having more opportunities to use their powers.)
Smarter Genies (BG2,BG2EE,BGT)
This component improves the various genies (djinni, efreet, and the like) in BG2. Mostly this is done by improving their scripts and systematising the rather chaotic list of spells and abilities that different genies get (in the original game, if you charmed a genie you'd see that it had a totally different list of spells from the ones it was actually using!) However, the component also changes summoned genies so that they count as "Gated" rather than "Summoned"; the practical consequence of this is that they are immune to Death Spell. This makes genie-summoning rather more useful.
As with the "Smarter Fiends", component, this component makes genies' spell use instantaneous and uninterruptable, and has an option to give genies a 50 percent hit point boost.
Smarter Celestials (BG2,BG2EE,BGT)
This component improves the way in which summoned devas and planetars use their magical and combat powers. It only affects celestials summoned by enemy NPCs, and it doesn't grant any extra abilities - it just uses the existing abilities more effectively.
As with the "Smarter Fiends", component, this component makes celestials' spell use instantaneous and uninterruptable, and has an option to give celestials a 50 percent hit point boost.
Smarter Dragons (BG2,BG2EE,BGT)
This component improves the intelligence of all the dragons in the game (including Adalon and Fll'Yissetat, but Abazigal is only modified if you also install the "SCS AI for Ascension" component). It tries to do this without granting them new abilities (the main grey area is exactly how many spells dragons should have: the unmodded game is somewhat inconsistent about it). At any rate, in play you should - hopefully - see dragons being a bit more discerning with their targeting and their spell priorities.
The component also systemises dragons' immunities to be consistent through the game, modifies dragon breath to penetrate magic resistance (the unmodded game is a bit inconsistent on this point, but since the spell Dragon's Breath goes through MR, presumably real dragon breath should too!) and lets dragons cast spells at a more realistic level (usually 15-25 or so).
As with the "Smarter Fiends", component, this component also lets dragons cast their spells instantly and uninterruptably.
The component has an option to increase dragon hit points very substantially - tripling them, in fact. At the moment dragons have about 200 hp, which by the late stages of Shadows of Amn really isn't enough to go toe-to-toe with an entire party. Somehow, it doesn't seem right that dragons have to rely on Stoneskin and Protection from Magic Weapons - this component gives them the ability to hang around in battle for longer.
Smarter Beholders (BG2,BG2EE,BGT)
This component upgrades the AI of the beholders, gauths, elder orbs and hive mothers in SoA and ToB. (It basically tries to do it non-cheesily, but it's hard to define this exactly since beholder powers are almost all scripted). Beholders get to use their eyestalks once per round each, but they will tend to manage to get through more of them in a round; their targeting has also been drastically improved (the new scripts are about 150 times the length of the old ones!)
In accordance with PnP 2nd edition rules, beholders are now immune to most (not all) of their own eyestalks, which makes them more willing to bombard their way through Spell Deflection. I have removed the Disintegrate eyestalk power (I don't like scripting for powers that require you to reload on a failed save) but I have added a Telekinesis eyestalk (more for fun than for increased challenge). And I have borrowed, with thanks, the Quest Pack component which allows beholders to lose their eyestalks when damaged. Beholders are also unable to use eyestalk powers when blinded (although their allies may use anti-magic rays to remove the blindness).
Hive mothers use the same range of powers as in the original game, but use them more efficiently, and use their eyestalks in the gap while they're waiting to cast spells again. Elder orbs were tricky because of the rather inconsistent range of powers they show in the unmodded game, but I have interpreted them as casting spells just as standard mages do, and as knowing 2 spells of each level. Their choice of spell, and of Contingency, Spell Trigger et al, has been optimised more, and they too use eyestalk powers while waiting to cast again (and show a preference for short-casting-time spells, so as to allow more eyestalk use.)
It might be worth noting that, even in the unmodded game, hive mothers can see through invisibility (though elder orbs cannot).
Beholder eyestalk rays ought to be able to work their way through Spell Turning spells and the like: a few beholder rays ought to be enough to overwhelm a Spell Turning spell (and for that reason, beholders are scripted to use their rays even on protected characters). However, for whatever reason this doesn't seem to work very well in-game. So instead, beholder rays now have a random chance (thirty percent) of dispelling a spell protection on contact; this should work out, on average, to the same thing. This is optional: you can choose whether or not to let beholder rays "burn through" defences in this way.
In addition, you can choose at install time to have beholders use an alternative form of their antimagic ray. In pen-and-paper D&D, a beholder's eyestalk blocks all magical effects, beneficial or otherwise, on the target for as long as it's targetted. In BG2, the eye is more powerful: it removes all magical effects, blocks spellcasting for several rounds, but doesn't block enemy magic attacks (including the beholder's other eyestalks). Optionally, the beholder antimagic ray blocks all magical effects, including harmful ones, for one round, and also disables magical activity (spellcasting etc) by the target for one round; this is supposed to simulate the beholder bathing the target with its antimagic ray for one round. This subcomponent obviously requires different scripting, so beholders will use their antimagic ray a bit more cautiously if it's installed.
Finally, if Spell Revisions is installed then Beholders will use a Spell-Revisions-style disintegrate ray (at 10th level for ordinary beholders, 20th level for Hive Mothers). The default in this case is that they do use Disintegrate; entering CLUAConsole:SetGlobal("DMWWBeholderDisintegrateSR","GLOBAL",1) will disable it.
Smarter mind flayers (BG2,BG2EE,BGT)
This component improves the intelligence of the mind-flayers and their kin (specifically, it upgrades flayers, ulitharids, vampiric illithids, and the Master Brain). It allows the illithids to use a somewhat wider range of abilities than before (notably, they have access to a few physical psionic attacks, like Ballistic Attack, and they can astrally travel to more convenient bits of the battlefield); it significantly improves their targetting; it allows them to use each power every 2-4 rounds and choose the most appropriate available power; it lets them avoid attacking targets who are immune to their abilities or to their physical attacks.
There are a variety of options in this component. You can choose whether to let mind flayers see invisible opponents (I'm inclined to think that their great intelligence and wide range of psionic powers means that invisibility is no barrier to them; not everyone agrees, though). You can also choose to give mind flayers 50% resistance to melee and missile damage. (The Tactics version of smarter mind flayers grants both these powers; both are optional in SCS.)
The component also makes a few changes in how psionic powers work. It mildly increases the damage done by physical psionic attacks (though not to anything like the extent that Tactics does) and it changes "anti-psionic" items so that they do not protect from physical psionic attacks. (On my interpretation, "Ballistic attack" involves using psionics on a rock, not on a PC). This gives illithids a few more options when facing enemies who are shielded from mental attack. The component also systematises illithid magic resistance and level, so that all of them are 90% magic resistant (previously there were a few exceptions) and the same level. As of version 16, it allows illithids' detonation power to destroy skeletons automatically (in accordance with the 2nd edition rules, as it happens). (This can be disabled at the console.)
If the "Smarter Mages" component and this one are both installed, the Alhoon is also upgraded. I interpret him as a L18 mage with the psionic powers of an ulitharid, I also give him the "split mind" psionic power, which allows him to cast a spell and use a psionic power in the same round. (Yes, purists, this is a valid 2nd edition psionic power!) This guy is now fairly dangerous.
Improved Vampires (BG2,BG2EE,BGT)
This component upgrades vampires' intelligence and abilities, roughly in line with pen-and-paper Dungeons and Dragons. They should target their magic more effectively, pick on people vulnerable to their level drain, and so forth. The component also standardises vampire statistics a bit (usually increasing vampire ability scores slightly). It allows vampires to summon wolves, bats, or rats (the bat summoning was present in earlier versions but has been toned down), to drink blood (which drains Constitution) as well as draining levels, and to make much more use of their various shapeshifting abilities (bat, rat, wolf, gas cloud).
This component does affect Bodhi, but only if you don't install the "Improved Bodhi" component (in other words, if you want Bodhi to use her original-game abilities more effectively but don't want to give her the extra powers of that component, install Smarter Vampires but not Improved Bodhi).
Smarter Githyanki (BG2,BG2EE,BGT)
This component improves the githyanki in the game, mostly through better scripting for their psionic powers (those which they demonstrate in-game in one way or another), although it does also slightly raise the level of some of the stronger gith. It also makes the same general upgrade to psionics that the "Smarter Mind Flayers" component does. Finally, it upgrades the githyanki lair in ToB by the rather simple expedient of opening all the doors. ("Sir, just a suggestion, but maybe we should fall on our enemies all at once rather than dividing our forces into four bite-sized chunks?")
Smarter ToB final villain (BG2,BG2EE,BGT)
This component upgrades the AI of the final villain of Throne of Bhaal, in both their Ascension and non-Ascension forms. I try fairly hard to use only those abilities actually demonstrated in-game, although I do fix a bug in the non-Ascension version whereby their last form wasn't using quite the right script.
Smarter Illasera (BG2,BG2EE,BGT - requires Ascension)
This component changes the AI of the Ascension version of Illasera (and her flunkies) to match the SCS norm. Hopefully this makes them more rather than less dangerous (although Ascension AI is pretty good, so I'd welcome feedback).
This component has no effect on the non-Ascension version of Illasera (who is a standard fighter/mage and gets modified by the "Smarter Mages" component). Both the original and the finale versions are affected.
Smarter Yaga-Shura (BG2,BG2EE,BGT - requires Ascension)
This component changes the AI of the Ascension version of Yaga-Shura (and his flunkies) to match the SCS norm. Hopefully this makes them more rather than less dangerous (although Ascension AI is pretty good, so I'd welcome feedback). Both the original and the finale versions are affected.
This component has no effect on the non-Ascension version of Yaga-Shura (who is a standard fighter and gets modified by the "Smarter General AI" component).
Smarter Abazigal (BG2,BG2EE,BGT - requires Ascension)
This component tries to upgrade the AI of Abazigal. Both his humanoid and dragon forms are affected; if you have Ascension installed, so is the finale form of Abazigal, and so is his companion Tamah. I try to systematise Abazigal's magical talents a bit, but I don't do anything for which there isn't some existing in-game justification.
Smarter Gromnir (BG2,BG2EE,BGT - requires Ascension)
This component changes the AI of the Ascension version of Gromnir Il-Khan (and his flunkies) to match the SCS norm. Hopefully this makes them more rather than less dangerous (although Ascension AI is pretty good, so I'd welcome feedback). Both the original and the finale versions are affected.
This component has no effect on the non-Ascension version of Gromnir (who is a standard fighter and gets modified by the "Smarter General AI" component).
Ascension versions of Irenicus and Sendai use SCS abilities and AI (BG2,BG2EE,BGT - requires Ascension)
Ascension demons use SCS abilities and AI (BG2,BG2EE,BGT - requires Ascension)
These components do exactly what they say: they modify these aspects of Ascension to fit the SCS norm. (Note that only the chapter 10 version of Sendai is affected: the chapter 9 version will use SCS scripting anyway.)