Mana

Mana is the recurring second player resource, which, unlike Life, reflects the amount of energy that a character has. It is used for casting spells or applying abilities, draining mana with every cast, more powerful spells consuming more mana.

If mana is too low, casting the costly spells will be temporarily disabled, until the character has generated enough mana again. Mana bar sphere is depicted as a glass orb filled with bright blue glowing liquid in all three games.

Diablo I

Diablo I Mana orb

In Diablo, the amount of maximum mana is affected by items with mana or Magic attributes.

Mana does not recover over time, so the player will need to find a Mana potion to refill it, or use "Hit Steals Mana" (suffixes The Bat, Vampires). In Hellfire, speaking to Adria refills Mana as well.

The Mana cost of a spell or skill may (but is not guaranteed to) change with spell or skill level. Generally, it can drop up to 50% of base value (with some exceptions).

Diablo II

Diablo II Mana Orb

In Diablo II, mana slowly regenerates by itself. Maximum mana and its regeneration rate can be affected by certain item attributes, skills (Warmth, for example), and some Shrines.

Some monsters' attacks, like Baal's abilities or Finger Mages' strikes, may drain the character's mana, leaving them severely weakened in battle.

With enough points, some skills' mana cost may be reduced to zero, making a skill free to use. Most spells and skills, however, consume more Mana as they grow more powerful.

Mana generating item modifiers

The following modifiers can be found on items, most often on Magic Items in the form of prefixes and suffixes. Hirelings do not have a mana pool and will not grant the player any bonus mana from these either.

• "Points of Mana After Each Kill" (prefixes Triumphant, Victorious) provides a small amount of mana every time the player kills an enemy. Any type of damage inflicted by the player works, kills by minions do not.
• "Damage taken Goes to Mana" (prefix Vulpine) generates mana at a percentage of the damage inflicted against the player. So if an item provides you with a 10% Damage taken Goes to Mana modifier, and you receive 40 damage, you will gain 10% * 40 = 4 mana.
• "Mana Stolen Per Hit" (suffixes Bat, Wraith, Vampire) steals mana equal to a percent of the damage you inflict. So 5% Mana Stolen will return 5% of the damage you do to a monster. Mana steal only works on Melee and physical ranged attacks.

Diablo Immortal

Mana was initially present in Diablo Immortal, but was removed and replaced with a cooldown system.

Diablo III

"Witch doctors’ inborn connection to the Unformed Land allows them to tap into a deep well of spiritual energy, called Mana. Mana is a vast but slowly-regenerating resource; witch doctors must be choosy with their attack spells and hexes to ensure that they don’t leave themselves depleted of power and exposed to enemy attacks. Since Mana returns ponderously, witch doctors conserve it by relying on semi-permanent additions to their arsenal, such as their summoned mongrels and the horrific gargantuan, which can offer protection and chew through enemies without any further mana cost. Witch doctors have a sizeable reservoir of energy to call upon at once, and, when they need to, they can deploy immense blasts of destructive force and cut a swath across nearly any battleground in a short period of time."

- Game Guide^(src)

Witch Doctor's Mana orb

In Diablo III, only Witch Doctors have Mana due to balancing reasons. In exchange, the classes have alternative resources that have different ways of regenerating (for example, the Monk has Spirit, which generates points for every Primary attack he lands).

A Witch Doctor's inborn connection to the Unformed Land allows them to tap into a deep well of spiritual energy, called Mana. A Witch Doctor may have up to +450 Mana from items (+600 with legendary items), and +42 Mana regeneration (+7 more from Kormac). Spiritual Attunement grants 10% maximum Mana and 1% Mana regenerated per second, while other active and passive skills may recover Mana on kill (or from health globes), change Mana costs (from -10% to +30%), recover it when activated, refund Mana when cast, or increase effective Mana regeneration (up to 30%). Mordullu's Promise makes Firebomb generate additional 100-125 Mana when cast. Paragon levels may grant +200 more Mana. Rush of Essence is unique in that it causes each Spirit spell cast to restore a fixed amount of Mana, regardless of its cost, effectively making these spells free to cast.

Since Mana recovery rate is low relative to other resources, Witch Doctors may easily run out of it in battle. However, they may choose to discharge all their most powerful spells at once and pray that would be enough. The alternate way is to rely on pets, which do not have Mana cost.