Lifesteal

Lifesteal (or sometimes referred to as Lifeleech) is a passive ability that allows the attacking unit to gain Health when attacking an enemy unit. The lifesteal ability can be gained via items, passive abilities or the auras of other units.

Lifesteal Unique Attack Modifier
This is the most common form of lifesteal and can be used by both melee and ranged units. Items that give this type of lifesteal are:
 * Morbid Mask 15% Lifesteal
 * Helm of the Dominator 15% Lifesteal
 * Mask of Madness 17% Lifesteal
 * Satanic 25% Lifesteal (unactivated), 175% Lifesteal (activated)

These items do not stack with each other. The one in the highest priority slot will override the others.

Lifesteal Aura
Lifesteal granted by an aura gives all melee units in the area of effect the lifesteal ability. Ranged heroes do not benefit from this aura. Lifesteal auras stack with different lifesteal auras, but not with identical lifesteal auras. Lifesteal auras are not unique attack modifiers, so they also stack with lifesteal granted by unique attack modifiers.

Items and skills that provide a Lifesteal Aura are:
 * Vampiric Aura (Skeleton King): (15%/20%/25%/30% with 900 area of effect, affects allied and self owned melee units)
 * Vladmir's Offering: (16% on a 1100 area of effect, affects allied and self owned melee units)
 * Insatiable Hunger (Broodmother): (40%/60%/80%, affects self only)

Damage and Lifesteal
The amount of health a unit gains from lifesteal is calculated after all damage reductions.
 * Critical Strike: Lifesteal is calculated after Critical Strikes, which means that it will increase the amount of life you steal.
 * Bash: Melee bashes (which deal magical damage) will not interact with lifesteal. Ranged Bashes (which deal physical damage) will interact with lifesteal.
 * Lifesteal will only work on the main target of the attack, abilities that cause an attack to hit more than one target (Cleave or Splash) does not add extra lifesteal, despite what the animation might show.

Triggered Lifesteal
Certain lifesteal effects were written as triggered effects in the original Warcraft III engine. While such nuances are moot as of Dota 2, the following spells still behave differently than other lifesteal effects:
 * Feast (Lifestealer): 4%/5%/6%/7% of the current target's life on attack.
 * Feast damage is reduced by armor, although the heal is not. Although Feast is not a Unique Attack Modifier, it will not interact with other attack modifiers such as Critical Strike.
 * Open Wounds (Lifestealer): Recover 15%/20%/25%/30% of all damage dealt for 8 seconds.
 * Open Wounds is unique in that it will grant allies lifesteal on the target while also healing Lifestealer for a portion of all damage dealt. All damage dealt can grant lifesteal, including spell damage.