Difficulty

Difficulties are intended to increase the replay value of the Diablo franchise by offering a greater challenge. Players can attempt to play the game in another tier, featuring penalties for their character while making the monsters more difficult to defeat. The result of adventuring in these tiers is not only the greater challenge, but also the possibility of greater rewards. This is voluntary, and players can return to an easier difficulty level should they choose so. The subsequent games also adopted this idea, however, featuring greater complexity with each iteration.

Diablo I/Hellfire
The original Diablo and its non-canon expansion, Diablo: Hellfire, have three difficulty levels. While the original game's higher difficulties could only be experienced online outside of cheating, Hellfire allowed higher difficulties in singleplayer games.

Normal
Characters created in the original Diablo start in the difficulty mode. Excluding a certain trick that requires an already leveled multiplayer hero, Normal difficulty is the only difficulty accessible in the original game if the hero is in singleplayer mode. Multiplayer heroes must grow in power if they wish to start/join a game on the harder difficulties.

The Hellfire expansion pack permits any hero access to and  difficulties, even if he/she is a singleplayer hero. In addition, if the hero is in singleplayer mode, the game does not require them to grow in power for these levels. Choosing to go into a higher difficulty early on, however, is considered insanely suicidal or insanely bold, as the hero will have quite a hard time surviving in the depths of the labyrinth.

Nightmare
This level is present in the multiplayer mode of Diablo I as well as Hellfire. In both cases, the monsters will possess at least three times the health they would have possessed on Normal difficulty, and players will need at least +80% to Hit and +80 Armor Class to dish out/avoid damage like they would do in Normal. In Diablo I, the monsters also receive +1 to their Hit Points after the modifiers, while in Hellfire, the monsters receive +50 to their Hit Point capacity after the initial x3 difficulty bonus, making the foes even hardier than they are in the regular Diablo.

Hell
While both versions of the original Diablo and Hellfire have differences between them, there are several identical aspects; monsters will deal even higher damage per hit, and their Hit Point capacity is increased by at least x4. Players will need at least +120% to hit and +120 Armor Class to dish out/avoid damage like they would do in Normal, and monsters have grown even hardier to the effects of magic, many monsters even possessing resists and/or immunities which otherwise wouldn't on other difficulty levels.

In the original Diablo, monsters have their Hit Point capacity increased by x4 compared to Normal mode, and receive +3 HP to their totals after the multiplication occurs. In Hellfire, they possess a +100 bonus after the multiplication, resulting in foes with at least 100 Hit Points even in the Cathedral section.

It should also be noted that suffering melee damage from the later monsters on Hell difficulty will stun you, no matter your level or class. Players are better off avoiding most attacks rather than reducing the damage dealt per blow. This is more apparent in the regular Diablo, because there are no classes that possess a stun threshold higher than 1 point per level, and because of no Reflect.

Casters should be aware that their spell planning will need to be adjusted for Hell Difficulty. There are even monsters which are immune to all elements of spell damage, resulting in a greater dependence on Golems and Stone Curse.

Diablo II
Diablo II and its expansion, Diablo II: Lord of Destruction, both featured the same three difficulty tiers as in the previous game.

Normal
Characters that are created will start on this difficulty level. Hirelings and Summons deal 50% damage to Act Bosses on this difficulty. If a character kills Diablo in the non-expansion, they will gain a new title and the option to venture into Nightmare upon starting the game. Expansion pack players will instead receive the title upon successfully defeating Baal, as well as the opportunity to adventure in the Secret Cow Level.

In the classic, playing without the expansion, either by not installing Lord of Destruction or leaving the checkbox blank during character creation, male characters will be titled Sir and female characters Dame. Hardcore will grant Count to male characters and Countess to female characters. With the expansion, the titles will be Slayer for Softcore and Destroyer for Hardcore.

Nightmare
While death in Normal will rob you of a sum of gold from the Stash, Nightmare will also take 5% of your current level's experience points away for dying; you can recover 75% of that total by retrieving your corpse. This does not affect Hardcore heroes, as death prevents the character from ever being played again.

In classic Diablo II, male characters will be titled Lord and female characters Lady. Hardcore will grant Duke to male characters and Duchess to female characters. In the expansion, the titles will be Champion for Softcore and Conqueror for Hardcore upon defeating Baal. Players will now have access to Hell difficulty, where they will face the greatest challenges that the game has to offer, but also the opportunity for the very best loot.

The changes between Normal and Nightmare are as follows:


 * Increased monster levels and stats (hit points, defense, damage, resistances, etc.)
 * Player and Hireling resistances are reduced by –40% in the expansion. Classic Diablo II players only suffer –20% to all resists, but have fewer means to combat them: no Charms, Runes, Jewels, or Scrolls of Resistance.
 * Hirelings and Summons deal 35% damage to Act Bosses.
 * Duration of Freezing and Chilling effects and AI-affecting curses are reduced by 1/2.
 * Life and Mana Leech effects are reduced by 50%.
 * Static Field cannot reduce a monster's health below 33%.
 * Many maps' areas are increased in size.
 * Act V has additional "Guest Monsters" from other acts to increase the variation.

Hell
As in Nightmare, dying will also take experience away, though now increased to 10%. Again, it does not affect Hardcore heroes, who cannot come back from death to begin with.

In classic Diablo II, male characters will be titled Baron and female characters Baroness. Hardcore will grant King to male characters and Queen to female characters. In the expansion, after defeating Baal in Softcore, male characters gain the title Patriarch while female characters gain the title Matriarch; in hardcore, all characters gain the title Guardian.

The Über Tristram and Diablo Clone events can only be completed on Hell difficulty.

Differences between Normal and Hell include:
 * Further increased monster levels and stats.
 * Nearly all monsters have at least one Immunity and additional Resistances.
 * Player and Hireling resistances are reduced by an additional 60%, for a total of –100% in the expansion. Classic Diablo II players only suffer –50% to all resistances, but have fewer means to combat this: no Charms, Runes, Jewels, or Scrolls of Resistance.
 * Death results in a loss of 10% of the experience required to reach the next level. Retrieving your corpse restores 75% of the lost experience.
 * Hirelings and Summons deal 25% damage to Act bosses.
 * Duration of Freezing and Chilling effects and AI-affecting curses are reduced by 3/4.
 * Life and Mana Leech effects are reduced by 2/3.
 * Static Field cannot reduce a monster's health below 50%.
 * Many maps' areas are much larger in size.
 * Act V has additional "Guest Monsters" from other acts to increase the difficulty.

Trivia

 * As of 2019, the record speed of completing all three difficulties from a fresh start is 2 hours 43 minutes.

Development and Release
Like its predecessor, Diablo III featured Normal, Nightmare, and Hell difficulties. However, it was found by many to be either too easy or too difficult, so by release of 2.0, difficulty levels were made more complex, but also much more suited to an individual's playing ability.

Inferno
Upon release day, Inferno was the final difficulty mode. The lowest monster level found here was 61, which is 1 level higher than the level 60-cap for player characters. Monsters increased by one additional level for every act, up to lv. 63 in Act III.

2.0/Reaper of Souls
As of the pre-expansion patch for Diablo III, Normal, Hard, and Expert are unlocked at the start, Master requires the player to either destroy Diablo or reach level 60, and Torment requires a hero at level 60. The way the game's actual difficulty works depends on that of the host's character level. That is to say, as a hero levels up in power, so do his/her enemies. The bonuses granted by increasing difficulty are as follows:


 * Normal: No bonuses, due to being the default difficulty.
 * Hard: +75% Experience, +75% Gold Find
 * Expert: +100% Experience, +100% Gold Find
 * Master: +200% Experience, +200% Gold Find
 * Torment I to XIII (see main article for details)

In addition, starting from Expert onwards, Bounties give double Blood Shards. Master and Torment I+ allow monsters level 61+ to drop Imperial quality gems. Torment I+ allows new Legendary Items to be found at level 70, and gives a specific bonus to finding those items, scaling with increased difficulty (approximately 15% with each level, stacking multiplicatively).

On Torment difficulty, if the Nephalem takes too long (usually over 3 to 4 minutes) to defeat most of the game's bosses, they become Enraged, greatly lessening the hero's odds of achieving victory. For exact details on an Enrage timer, see the bosses' individual pages. There are two types of enrage effects: a soft enrage (the combat grows more difficult the longer it lasts, up to the point where it becomes overwhelming) and a hard enrage (once the time is up, it becomes much harder, if not impossible, to defeat the boss without overpowered gear). If a player wishes to avoid these effects, tracking their effective DPS is advised.

Note that a hero's gold find is multiplied by the difficulty level's bonus. As an example, a hero who has a equipped (+100% gold, or 2x) on Expert difficulty (also +100%, or 2x) will receive a total of +300% (4x), not just +200%.