Characters can be immune to most of the negative effects. For example, a character with disease immunity will almost never need fear the negative effects of disease. This is only “almost” though, as there are some unusual cases in which immunities can fail. These range from the devious (a script can often find ways around immunities, such as implosion ignoring immunity to death magic) to the accidental (for example, a bug causes long-term spells to be treated as the last spell cast with regards to immunity by spell level).
A character can have immunity to damage as well. The two types of damage immunity effects are increase and decrease. (“Decrease” is also known as vulnerability.) These immunities are specified as a percentage of damage, and the percentages are capped at 100%. If a character has multiple immunities against the same element they are added together, any additional immunity above 100% has no effect. This percentage is multiplied by the damage received to obtain the amount subtracted from (for immunity) or added to (for vulnerability) the damage amount. As long as the net immunity is above zero, there is a minimum of 1 point subtracted (absorbed).
Examples: “Fire 90% Damage Immunity – Increase” will cause 10 points of fire damage to be reduced by 10×90% = 9 damage, resulting in only 1 point of damage actually being inflicted. “Cold 100% Damage Immunity – Decrease” will cause 10 points of cold damage to be increased by 10×100% = 10 damage, resulting in 20 points of damage actually being inflicted. “Piercing 75% Damage Immunity – Increase” combined with “Piercing 50% Damage immunity – Increase” would be added together 75%+50% = 125% immunity to piercing damage, resulting in no piercing damage being inflicted (100 piercing damage would inflict 0 hit point loss). “Fire 50% Damage Immunity – Increase” Combined with “Fire 50% Damage Immunity – Decrease” would be added together 50%-50% = 0% immunity to fire damage, resulting in normal fire damage being inflicted (100 fire damage would inflict 100 hit point loss).