Quests are a series of missions of which most are integral to proceeding in the single-player game. Most can be skipped, only a few are truly necessary to complete to advance in the game. Still, many quests may offer good rewards for completing them, so many players opt to complete them at later points in the game if they did not the first time through.
Each act has at least one quest that must be completed in order to progress, and that is the boss kill quest that requires the player to kill a Great Evil. For each of the five acts, these are:
- Sisters to the Slaughter: Kill Andariel
- The Seven Tombs: Kill Duriel
- The Guardian: Kill Mephisto
- Terror's End: Kill Diablo
- Eve of Destruction: Kill Baal
Some acts have other quests that are necessary to complete. In these cases, these quest must be finished in order to reach the area the act boss is in. They can be seen as prereqs for the last quests of each act
- The Horadric Staff and The Arcane Sanctuary are both needed in order to reach Tal Rasha's Tomb where Duriel is.
- The Blackened Temple must be completed before the player can enter the Durance of Hate in that difficulty.
- Rite of Passage must be finished before the player can enter Worldstone Keep in that difficulty.
- Act I and Act IV have no other mandatory quests.
The quests listed above are required by the game code to be completed. However if they player plays singleplayer, some become almost mandatory since they cannot be skipped by advanced players opening Town Portals ahead of the game (and they are a lot more appealing to do as you are faced with them anyway).
Some quests are also hard to miss completing. For example, The Summoner is technically not mandatory, but he appears right next to the book that needs to be read to complete the actual mandatory quest, The Arcane Sanctuary. So while a player can technically run past The Summoner and just read the book, most will kill him while they are there.
There are several optional quests that players will probably wish to finish even though they are not mandatory. These quests offer tangible rewards.
- Den of Evil, Radament's Lair and The Fallen Angel all three give the player extra skill points when completed. These are of great help to all characters and should always be finished no matter what build or difficulty, for a total of 12 extra skill
- In Act III, The Golden Bird, and Lam Esen's Tome quest are useful as they add 20 health points and 5 stat points respectively, each difficulty.
- In Act IV, The Hell's Forge quest will give you several high quality gems and a decent chance at a mid to high rune.
- In Act V, The Siege on Harrogath will allow you to add a socket to any non-socketed item, and The Prison of Ice quest will grant you a passive +10 to all resistances bonus (+30 in total once completed at all difficulties).
List of Quests
Act I Quests
|The Sightless Eye|
|Den of Evil||Sisters' Burial Grounds||The Search for Cain||The Forgotten Tower||Tools of the Trade||Sisters to the Slaughter|
Act II Quests
|The Secret of the Vizjerei|
|Radament's Lair||The Horadric Staff||The Tainted Sun||The Arcane Sanctuary||The Summoner||The Seven Tombs|
Act III Quests
|The Infernal Gate|
|The Golden Bird||Blade of the Old Religion||Khalim's Will||Lam Esen's Tome||The Blackened Temple||The Guardian|
Act IV Quests
|The Fallen Angel||The Hellforge||Terror's End|
Act V Quests
|Lord of Destruction|
|Siege on Harrogath||Rescue on Mount Arreat||Prison of Ice||Betrayal of Harrogath||Rite of Passage||Eve of Destruction|