Diablo II's storyline progresses through four chapters or ""Acts"". Each act following a more or less predetermined path, although there is some random-level generation in wilderness areas and dungeons between key cities. There are a list of quests which are usually required to advance the story, though some are optional. In contrast to the first Diablo whose levels consisted of descending deeper and deeper into a Gothic-themed dungeon and Hell, Diablo II's style is much more varied. While Act I is similar to the original, Act II mimics canaan desert while Act III is supposedly based on the Maya civilization jungles. Act IV takes place in Hell and is the shortest, with just three quests compared to the other Acts that have six. The Lord of Destruction expansion adds Act V which continues the story where Act IV left off.
In addition to the acts, there are three sequential difficulty levels: Normal, Nightmare, and Hell; completing the game (four Acts in the original or five Acts in the expansion) on a difficulty setting will open up the next level. On higher difficulties, monsters are stronger and are resistant to an element, experience is penalized on dying, and the player's resistances are handicapped. However, better items are rewarded to players as they go through higher difficulties. A character retains all abilities and items between difficulties, and may return to a lower difficulty at any time.
Players can also create a hardcore character. In normal mode, the player can resurrect their character if killed and resume playing, while a hardcore character has only one life. If killed, the character is permanently dead and unplayable, and all items and equipment on that character will be lost unless another friendly character has the ""loot"" icon checked.