Mechanics (2)

Understand Armor Class (AC): This measures how difficult you are to hit in combat. AC starts at 10 and decreases, with more negative numbers being better. A bonus to AC lowers your AC value.

Grasp THAC0 (to hit armor class 0): This determines your probability of hitting an opponent with a twenty-sided die (d20). For example, a ninth-level Fighter or thirteenth-level Cleric has a THAC0 of 12, meaning they hit on a roll of 12 or higher before armor modifiers. An opponent with AC -2 would require a roll of 14 or greater (14 - 2 = 12), while an opponent with AC 1 would require a roll of 11 or greater (11 + 1 = 12).

Learn Saving Throws: The same d20 roll used for attacks is used for saving throws against magic. You must roll equal to or greater than your saving throw value to resist or reduce magical effects. For instance, a saving throw of 16 vs. spells gives you a 1-in-4 chance of success. Saving throws decrease as your character gains levels. Different saving throw values exist for various attack types.

Understand Spellcasting: Unlike games with a mana pool, magic in Baldur's Gate II: Shadows of Amn uses a finite number of spells. Once cast, a spell is unavailable until you rest. Mages can only cast spells they know, which are acquired by finding or buying scrolls and writing them into a spellbook.

Consider Weapon Speed: Weapon speed is a number between 0 and 10, with lower being better, and it dictates attack order. Casting time for spells is equivalent to weapon speed. Casting a spell with a long casting time from a safe distance is advisable, as being hit can interrupt your spell.

Note Attack Rate: Weapon speed is separate from attack rate, which depends on Fighter level and weapon skill. You start with one attack per combat round. At two points of weapon proficiency or level 7 Fighter, you gain an additional half attack per round. Two attacks per round are achieved with level 2 proficiency and level 7 Fighter. The maximum attack rate of 3 requires level 5 weapon proficiency and level 13 Fighter. Missile weapons have different base attack rates, such as one per round for a crossbow and three per round for darts.

Understand Levels: The term 'Level' can refer to a dungeon section, a character's power and spellcasting ability (e.g., a 12th-level Mage casts 6th-level spells), or general power (e.g., high-level loot).

Earn Experience Points (XP): Characters gain levels by earning XP from defeating enemies and completing quests. The XP required for each level increases exponentially. For example, a Fighter needs 125,000 XP for level 8 and another 250,000 XP for level 9. After certain levels (9 for warriors/divine spellcasters, 11 for Mages/Rogues), subsequent levels require a fixed XP amount, from 220,000 for Thieves/Bards to 375,000 for Mages/Sorcerers. XP is divided among party members, so smaller parties level up faster.

Manage Hit Points (HP): HP measures vigor. You see your HP, but only visual cues (Uninjured, Injured, Near Death) for enemies. Reaching 0 HP means death, though companions can be revived at a temple or with a spell. On Core Rules difficulty and higher, a blow sending a character deep into negative HP results in permanent death (a reload condition). On Story Mode, characters cannot die. On other difficulties, healing magic or resting is necessary for significantly injured characters.

Utilize Weapon Proficiency: To hit effectively, you must spend at least one proficiency point in a weapon. Using an unproficient weapon incurs a THAC0 penalty (2 for warrior types, 5 for mage types). Only single-classed Fighters can achieve proficiency levels higher than 2 in most weapons.