Getting a grip on the combat mechanics of this game is a distinct challenge, due to several counterintuitive and, in my opinion, unnecessarily complex aspects, directly inherited from its pen-and-paper ancestry. Still, I’ll try my best to make it intelligible. You can have up to six characters in the party, including your protagonist, and can directly control each of them if needed. Otherwise, you can assign a predetermined A.I. behaviour to any character you’re not controlling, so that they can take care of themselves in combat (otherwise, they won’t do anything until you specifically tell them to). E.g. the “Ranged” setting will make a character attack with any equipped ranged weapon and try to keep their distance from the enemies. You can toggle the A.I. on or off (helpful when you need to micromanage), and also select the entire party if you need everyone to move to the same location using two buttons at the bottom right of the screen. You can also choose between several battle formations, which allows you to place ranged characters in the back and melee characters at the front, for example.
Combat takes place in real-time, and all enemies are visible on the map. If you have a Ranger or a Thief, this allows you to scout ahead and plan for particularly large encounters. Battles are subdivided into six-second ‘turns’, which are individual to each character (the countdown starts from the moment you select an action for that character). Depending on their class and weapon proficiency level, a character can deliver a given amount of attacks per turn.
As far as combat statistics are concerned, the game’s pen-and-paper ancestry means that everything is calculated on the basis of various-sided dice (usually 20, but 4, 6, 8 and 10 are also used), from a weapon’s damage potential, to a character’s HP progression rate. It also means that some vocabulary such as ‘rolls’ or ‘Saving Throws’ has made it into the game. The latter are specific to each class and determine how well-protected a character is against certain negative effects: Wand attacks, Spells, Poison/Paralysis/Death attacks and Breath attacks (usually by Dragons). The lower the number, the better. This also applies to a character’s Armour Class, or AC (indicated by a shield symbol in the menu). This means that an AC of 2 is better than an AC of 4, and that an AC of -3 is better than both. A piece of equipment may indicate “AC bonus +1”, but in effect, it will lower the character’s AC by one point when equipped. You also get AC bonuses if your character’s Dexterity is 15 or higher.
THAC0 means “To Hit Armour Class 0”. This is the number a character would have to ‘roll’ on a 20-sided die to hit an enemy, if that enemy’s AC was 0. Basically, this determines a character’s accuracy. Again, the lower the better. So a THAC0 of -1 will be better than a THAC0 of 3. You also get THAC0 bonuses if your character’s Strength is 17 or higher. Additionally, for ranged weapons, a Dexterity of 16 or higher will grant another bonus to THAC0.
Weapon proficiency determines three things: the number of attacks per turn, damage bonuses and THAC0 bonuses. The higher the proficiency, the more attacks the character will deliver, the more damage they’ll deal, and the lower their THAC0.
As far as the class system is concerned, the most important distinction to understand is the one between dual- and multiclassing. A multiclassed character’s EXP is split between their two (or three) chosen classes. And while this means that they will gain levels in all their classes at once, the process will also be slower, and they will never reach as high a level as a single-class. They’ll also be limited to either one or two proficiency points per weapon, depending on the class combination chosen, and will not be able to pick a kit in the sequel for either of their classes. However, they will always have abilities from all their classes at their disposal (most importantly, this includes the High Level Abilities in the sequel), as well as a better choice of equipment. In terms of HP, they’ll gain half or a third of what each class would get whenever it levels.
Dual-classing can yield impressive results. However, you have to know what you’re doing, and there will be significant downtime, which doesn’t exist for multiclasses. In order to start, the character must reach level 2 in one class and meet some attribute requirements: a 17 in the main attribute of the first class (e.g. Strength for a Fighter) and a 15 in the main attribute of the second. You can start as whichever class you prefer (typically, the one you need the fewest abilities from), as long as the overall result is a valid combination. Once dual-classing is triggered, the first class goes dormant, and EXP goes to the second class only. So, if the character starts as a Fighter and duals to a Cleric, they will behave as a level 1 Cleric. Once the level of the second class overtakes the first, the first class reactivates. It won’t gain any more experience, but it will complement the second class, within the limits of that class’ restrictions; e.g. a dual-classed Fighter/Thief will be able to put five proficiency points into any weapon a Thief can use. The problem is that dual-classing too early is pointless (the benefits from the first class will be negligible), and dual-classing too late may leave you with an underlevelled second class. It’s a rather unforgiving system and, in my opinion, more of a hassle than anything. Besides, it entails playing a human character, which I’m just not interested in. The other difference between dual- and multiclassing is that you can choose to dual-class companions (Imoen being the usual suspect), but not to multiclass them.
Magic is subdivided into two types: arcane and divine, and each type includes offensive, beneficial and indirect spells, designated by red, blue and white symbols, respectively. Arcane magic is used by Mages and Bards, and divine magic by Clerics, Paladins, Druids and Rangers, which have overlapping, but slightly different spell selections. Paladins learn a smattering of Clerical spells, and Rangers some Druidic ones. Divine spells are learned automatically as the character gains levels and are not hampered by heavy armour. Some divine spells can also be cast directly from scrolls, although it must still be by a character whose class allows it. This notably concerns Lesser Restoration (which is the only way to quickly recover from Level Drain) and Raise Dead.
Arcane spells, on the other hand, cannot be cast if the user is wearing armour. This may cause some grief to Mage multiclasses, until you can get your hands on some decent robes. Moreover, arcane spells can only be learned by scribing scrolls, which isn’t automatic. A Mage’s or Bard’s Intelligence determines not only how many spells s/he may learn, but also the likelihood of successfully scribing a scroll. That is distinctly more aggravating, because if the character fails the scribing, the scroll will still be used up. I have no idea how that makes sense, but there you go. This unfortunately means that you should ideally save every time you plan to do some scribing, because even if you guzzle some Potions of Genius (which temporarily boost the user’s Intelligence), there’s still a chance of failure.
Since there’s no MP or mana, each spellcaster has access to several tiers of spells: seven for divine spells, nine for arcane ones. They can cast a certain number of spells per tier, which they can select at will from among the spells they know and which increases as they gain levels. Once they’ve exhausted their arsenal, they must rest in order to be able to cast again. They must also rest if they change their spell selection, in order to activate the newly-selected spells. This is a severely limiting system which forces spellcasters to be extremely conservative. So unless you want to have to rest between every battle, make sure they have some other means of attack for easy encounters. This is usually not a problem for divine spellcasters, Bards or multiclassed mages, but single-class Mages have to rely on subpar ranged weapons most of the time. Which is both frustrating and counterintuitive: if I’m playing a Mage, it’s so I can cast spells, not plink at the enemy with pebbles! That being said, the game also features various wands.These are infused with a variety of spells and allow a character to cast those spells a limited number of times. Anyone with a high enough Intelligence score may use them, but they’ll be at their best in the hands of a Mage. Still, I find it’s a poor compensation.
One more thing to watch out for is morale failure, something that you’re bound to encounter at least once if you’ve got Khalid in your party. If a character takes too much damage from a single hit (or if several other companions bite it), they’re liable to panic, become uncontrollable (their selection circle will go yellow) and start running around like a headless chicken. The only remedy is to wait until they snap out of it, but if there are traps or other groups of enemies nearby, this can lead to trouble.