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 pierced 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.

Physical immunity can be removed by using the Necromancer's Amplify Damage curse. The same ability of Decrepify curse wasn't verified yet, but if it has the ability to remove immunity it's 50% lowered physical resist is too weak (see below) against any monster with physical immunity.

It is important, that all known resist lowering skills are working with 1/5 effectiveness against monsters with 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.

Monster resistances can be viewed here: [1].