Fire Immunity is one of the many Unit Abilities available in Master of Magic.
When a unit with Fire Immunity is struck by Fire Damage or Immolation Damage from any source, its Defense score is temporarily raised to 
50 for purposes of blocking this damage. This means that it is exceptionally difficult (though still possible) to inflict Fire Damage or Immolation Damage on this unit.
Fire Immunity is a rather rare immunity, possessed only by 3 different Fantastic Units - all from the 
Chaos realm. It is not possible to add Fire Immunity to a unit that does not already have it.
Description[]
Fire is essentially a chemical reaction, causing an object to turn from solid matter into gas while releasing plenty of heat and light. As such, it is a destructive force that few creatures can overcome. Nonetheless, the magical nature of some creatures, closely associated with fire itself, allows them to be engulfed in flames without feeling any adverse effects whatsoever.
These creatures, originating from the Chaos Realm, are essentially made of fire, which would explain why they do not react to it like all other living creatures would.
Effect[]
Fire Immunity is a passive ability that protects a unit specifically from Fire Damage and Immolation Damage.
Whenever a Fire Damage or Immolation Damage attack is performed against a unit with Fire Immunity, the unit's Defense rating is immediately raised to 50. Therefore, the unit can make 50 
To Block rolls, blocking on average of 
15 points of Damage - an impressively-high amount. It is unlikely for any attack to actually get through this much Defense, and normally results in the unit taking no damage whatsoever.
There are many sources of Fire Damage and Immolation Damage in the game, including spells, special abilities and straightfoward attacks.
Sources of Fire Damage include:
- The Fire Bolt Combat Instant
Fire Breath attacks
Sources of Immolation Damage include:
- The Fireball Combat Instant
- The Flame Strike Combat Instant
- The Fire Storm Instant Spell
- The Meteor Storm Global Enchantment
- The Immolation ability (whether innate or through the Immolation Unit Enchantment)
- The Wall of Fire Town Enchantment
Whenever any of the above strikes a unit with Fire Immunity, it triggers the immunity as explained above. The Fire Bolt spell has the highest chance of causing damage to a Fire-Immune unit - but it is still a pitiful ~3% chance even when the spell is fully-powered, and is highly unlikely to cause more than 1 if any.
Note that the Fire-Immune unit's Defense score is raised only for the purpose of blocking damage from a Fire Damage or Immolation Damage attack. Once the unit has made its defense rolls against this specific attack, its Defense score is restored to normal.
Exceptions[]
The Game Manual, as well as some in-game data, suggests that the following attacks should deliver Fire Damage, but they do not. Thus, none of the following attacks will trigger a target's Fire Immunity:
- Attacks made by an Efreet, a Fire Elemental or a Fire Giant.
- Attacks made by a unit enchanted with Flame Blade or affected by Metal Fires.
- Attacks made by a Hero holding a weapon imbued with the "Flaming" Item Power.
- Hero Magical Ranged Attacks that are associated with the Chaos Realm.
Units with Default Fire Immunity[]
Fire Immunity is a rather rare type of immunity, possessed by no more than 3 different kinds of units by default. All of these are Fantastic Creatures from the Chaos realm:
Efreet
Fire Elemental
Fire Giant
Acquiring Fire Immunity[]
There are no known methods of adding Fire Immunity to a unit that does not already possess it. Thus, the three units listed above will be the only units to ever have Fire Immunity in any game.