Immunity

Immunity refers to a monster or player character being completely impervious to damage of one or more types, or to a specific Crowd Control effect. All attacks that use the specified damage type or apply the effect listed are resolved as normal, with normal chances to hit, but even if they reach the target, they may not affect the target in any way. Unlike Absorption, Immunity to damage also makes the target immune to all secondary effects of the attack prevented, and very often, to Crowd Control effects in general.

Diablo II

Some higher level monsters will have the bonus of Immune to X, with X being a type of damage. These creatures have total immunity to that damage, meaning they will not lose any hit points if hit with that type of attack. The types of immunities found on these monsters are as follows:

• Immune to Cold
• Immune to Fire
• Immune to Lightning
• Immune to Magic (These creatures won't suffer any damage when attacked with skills that deal magic damage)
• Immune to Poison
• Immune to Physical (These creatures won't suffer any damage when attacked with melee or ranged physical damage)

But there is a way to cause damage to these monsters:

Cold, Fire and Lightning immunity can be partially bypassed with the Necromancer's Lower Resist curse and with the Paladin's Conviction aura. Poison immunity can be broken only with using Lower Resist. Cold Mastery does not break Cold immunity, however.

Physical immunity can be removed by using the Necromancer's Amplify Damage curse. This is a good reason for a melee/physical ranged character wanting an item that offers a chance to cast Amplify Damage on hit, as without it, they're forced to either switch to a skill of a different element, or leave the foe alone altogether. Decrepify also has the same ability, but it is less effective due to its physical damage penalty being lower.

For Undead monsters, Physical Immunity may also be dealt away with using the Sanctuary aura.

All resist lowering skills work with 1/5 effectiveness when breaking an immunity.

Another important information is: Most monster immunities are above 100%.

Lightning Immune is the easiest to break, with its 100-110% resistance. With the conviction aura from infinity it can be pierced.

Fire Immune is a bit harder. It has normally about 110-130% resistance. The Conviction aura from Infinity can't break these immunities normally, but a paladin with higher Conviction can break these.

Cold Immune is the worst of all. It is commonly over 150% resistance. It is nearly unbreakable with the lowered effectiveness of resistance lowering effects.

Open Wounds will work against physical immune monsters once they have taken damage of any kind.

Monster resistances can be viewed here: [1].

Diablo III

Immunities return in Diablo III. While monsters very rarely, if ever, have complete immunities to specific damage types, players can become immune to damage using certain skills, like Serenity, or a Shield Pylon. Being immune to damage also makes the character immune to all other harmful effects, and may clear all existing ones, unless specifically stated otherwise.

Partial immunities to specific types of elemental damage can be achieved by wearing protective legendary amulets.