The Immune bit does nothing alone. It's thought that it's part of an incomplete plan to make Immune like Absorb, but Absorb goes into its single elemental byte where as Immune is a separate byte all around.
The Cursed Ring will Absorb any element that it also is paired with, so say you have the Fire Armor, you would then recover when hit by an Ice Attack since it resists Ice, go one step further and say you have the Dragon Shield, when that happens you absorb Fire, Ice, and Lightning Elemental attacks.
The Immune bit is also broken because it gives 99% evasion because of a lack of optimization (they save a certain bit of data to a place that is supposed to temporarily store, but never takes it out which leads to it being added to evasion.) I have a patch to fix this, Immune on its own does nothing, but when the Immune piece of gear also resists other elements, they then become Immune to them.
