Mechanics

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

Grasp THAC0 (to hit armor class 0): This is a measure of your probability to hit an opponent with a twenty-sided die (d20). For example, a ninth-level Fighter or thirteenth-level Cleric has a THAC0 of 12, meaning you hit on a roll of 12 or more before armor modifiers. An opponent with AC -2 requires a roll of 14 or greater (14 - 2 = 12), while an opponent with AC 1 requires 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. To succeed, you must roll equal to or greater than your saving throw value. For instance, a saving throw of 16 vs. spells gives you a 1-in-4 chance to avoid or reduce magic effects. Saving throws decrease as you level up, with different values for different attack types.

Understand Magic System: Magic uses a finite number of spells that are gone after casting until you rest. Mages can only cast spells they know and must acquire new spells by finding or buying scrolls to write into their spellbook.

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

Understand Attack Rate: Attack rate is based on Fighter level and weapon skill. You start with one attack per combat round. Reaching two weapon proficiency points or level 7 Fighter level grants an extra half attack per round. Two attacks per round require level 2 proficiency and level 7 Fighter levels. The maximum of three attacks per round requires level 5 weapon proficiency and level 13 Fighter levels. This applies to melee weapons; missile weapons have different base attack rates.

Understand Levels: 'Level' can refer to a dungeon section, a character's power and spellcasting ability, or general power (e.g., 'high-level loot').

Gaining Experience (XP): Characters gain levels by earning XP from defeating enemies and completing quests. XP required for levels rises exponentially. After certain levels (9 for warriors/divine spellcasters, 11 for Mages/Rogues), subsequent levels require a fixed XP amount, ranging from 220,000 (Thieves/Bards) to 375,000 (Mages/Sorcerers). XP is divided among party members.

Understand Hit Points (HP): HP measures vigor for you and enemies. You see your HP, but enemy HP is indicated by status (Uninjured, Injured, Near Death). Reaching 0 HP means death, though resurrection is possible at temples or via spells. On Core Rules difficulty and higher, falling into deep negative HP results in permanent death. Story Mode prevents character death.

Weapon Proficiency: To hit effectively, you need at least one proficiency point in a weapon. Using an unproficient weapon incurs a THAC0 penalty (2 for warriors, 5 for mages). Only single-classed Fighters can exceed proficiency level 2 in most weapons.