Mechanics

Understand Baldur's Gate II: Shadows of Amn's core mechanics, including AC, THAC0, saving throws, spellcasting, weapon speed, attack rates, levels, experience, and hit points.

Baldur's Gate II: Shadows of Amn utilizes the Advanced Dungeons & Dragons (AD&D) 2nd Edition ruleset, which may differ from modern RPG conventions. This guide explains the core mechanics.

AD&D Rules Explained:

Armor Class (AC)

A measure of how difficult you are to hit in combat. AC starts at 10 and decreases; a more negative AC is better. Bonuses to AC lower the value. AC acts as a modifier to an opponent's 'to hit' roll.

THAC0 (To Hit Armor Class 0)

Determines the probability of hitting an opponent with a twenty-sided die (d20). A ninth-level Fighter or thirteenth-level Cleric has a THAC0 of 12, meaning they hit on a roll of 12 or higher before AC modifiers. For example, against AC -2, a roll of 14 or higher is needed (14 - 2 = 12). Against AC 1, a roll of 11 or higher is needed (11 + 1 = 12).

Saving Throws

A d20 roll used to resist magical effects. You must roll equal to or greater than your saving throw value to succeed. A saving throw of 16 vs. spells gives a 1-in-4 chance of avoiding or reducing magic's effects. Saving throws decrease as you gain levels. Different saving throw values exist for different attack types.

Magic System

Unlike mana pools, magic uses a finite number of spells. Once cast, a spell is unavailable until you rest. Mages can only cast spells they have memorized from their spellbook, which is updated by writing down spells from scrolls.

Weapon Speed

A number from 0 to 10, where lower is better, determining attack order. Spell casting time is equivalent to weapon speed. Being hit during casting interrupts the spell.

Attack Rate

Independent of weapon speed, this is determined by Fighter level and weapon skill. Base is one attack per round. Reaching Fighter level 7 or two points in weapon proficiency grants an extra half-attack per round. Two attacks per round require level 7 Fighter and proficiency level 2. The maximum of three attacks per round requires level 13 Fighter and proficiency level 5. Missile weapons have different base rates (e.g., crossbows one per round, darts three per round).

Levels

The term 'Level' in D&D can refer to a dungeon section, a character's power and spellcasting ability, or general power (e.g., 'high-level loot').

Experience Points (XP)

Characters gain levels by earning XP from defeating enemies and completing quests. XP requirements increase exponentially per level. After certain levels (9 for warriors/divine casters, 11 for Mages/Rogues), subsequent levels require a fixed XP amount (220,000 for Thieves/Bards to 375,000 for Mages/Sorcerers). XP is divided among party members, so smaller parties level up faster.

Hit Points (HP)

HP measures the vigour of characters and enemies. Player HP is visible; enemy HP is indicated by descriptive states (Uninjured, Injured, Near Death). Reaching 0 HP means death, though resurrection is possible via temples or spells. On Core Rules difficulty and higher, taking damage that results in deep negative HP causes permanent character death ('blasted into chunks'). On Story Mode, characters cannot die. On other difficulties, significant HP loss requires healing or retreating to rest.

Weapon Proficiency

To use a weapon effectively, at least one proficiency point must be spent. Using an unproficient weapon incurs a THAC0 penalty (2 for warriors, 5 for mages). Only single-classed Fighters can achieve proficiency levels higher than 2 in most weapons. The Archer kit can attain Grandmastery.