Blizzard Damage is one of the many Damage Types in Master of Magic.
Blizzard Damage is essentially Area Damage. This type of damage is unique in that it makes separate To Hit rolls against each Figure in the enemy unit, instead of attacking only the "lead" figure (as would happen with Physical Damage types). The entire process is extremely complex, but the end result is that the more Figures there are in the enemy unit, the more damage it will suffer on average.
Blizzard Damage is distinct from the other Area Damage type, called Immolation Damage, in that it will trigger a target's Cold Immunity (if the target possesses this immunity), and will not trigger a target's Fire Immunity. Note that either of the two Area Damage types will trigger a target's Magic Immunity.
The name Blizzard Damage was chosen for this damage type because it best described its effect - despite the fact that the term "Blizzard" is not used anywhere in the game.
Blizzard Damage is delivered only by one source: the Ice Storm spell.
Blizzard Damage is a type of Area Damage, and as such is processed in a very complex way. Its purpose is to cause actual Damage Points to the target, but the way in which the game determines how many Damage Points are inflicted is not easy to explain. For a more thorough explanation, see Area Damage.
Against Single-Figure Units Edit
This starts with a single set of X To Hit rolls against the target unit, where X is the strength of the Blizzard Damage attack. Each roll that comes up equal to or lower than 30 is considered a "registered hit" against the target. The number of registered hits is tallied up and recorded.
Next up, the target unit makes a single set of X Defense rolls, where X is the target's Defense score. The result of each roll is compared to the target's To Block score, with each roll coming up equal to or lower than that score being considered a "successful block". The number of successful blocks is tallied up and recorded.
The game then subtracts the number of successful blocks from the number of successful hits. This is the amount of Damage Points caused to the target. If the total amount of Damage caused to a target (including damage carried over from previous injuries) surpasses the target's Health, then the target unit is destroyed.
For a more thorough overview of this process, check out the article on Physical Damage. Note again that this applies only when the target is a Single-Figure unit!
Against Multi-Figure Units Edit
Blizzard Damage behaves very differently whenever it strikes a Multi-Figure target. In this case, it behaves almost as though several separate attacks were directed against each Figure in the target unit separately! The process is very complex to understand, and so is covered in full in the Area Damage article. Nonetheless we'll attempt to explain it briefly below.
To start, the attack makes X To Hit rolls against each Figure in the target unit, where X is the strength of the Blizzard Damage attack. Each roll that comes up equal to or higher than 30 is considered a "registered hit", but only against the specific Figure it was directed against. Already this is very different from Physical Damage, where all To Hit rolls are directed against the "lead" figure in the target unit. The game records the number of hits successfully registered against each individual figure, separately.
Next up, each individual Figure in the target unit makes X Defense rolls, where X is equal to the target unit's Defense score. The result of each roll is compared to the unit's To Block score, with each roll that comes up equal to or lower than that score being considered a "successful block". Again, the game remembers the total number of successful blocks made by each figure, separately.
To calculate Damage, the game subtracts each figure's successful blocks from the number of hits registered against this specific figure. This is why hits and blocks were recorded separately. The result is the amount of "unblocked hits" directed at each specific figure. The game also makes sure to limit each of these results to between 0 and the figure's current Health (no figure can suffer less than 0 Damage, and no figure can suffer more Damage than it has Hit Points).
Finally, all of these "unblocked hits" are pooled together. The sum of these unblocked hits is the total amount of Damage caused to the target. This is applied one point at a time, starting with the "lead" figure in the unit. It will kill off Figures as necessary, and will stop only when either all "unblocked hits" have been applied, or once the target has lost all of its Figures.
The result is usually massive damage to the Multi-Figure unit. If the Blizzard Damage was powerful enough, and the rolls involved were not particularly in the target's favor, Blizzard Damage can wipe out an entire Multi-Figure unit instantaneously - something which Physical Damage is highly unlikely to achieve.
Again, for a full analysis of this process, refer to the article on Area Damage, which explains this in much greater detail, including examples.
In case the target possesses only Cold Immunity, its Defense score is temporarily raised to 50 for purposes of blocking this Blizzard Damage. This will likely block any Blizzard Damage directed at the unit. The chance of any damage from an Ice Storm getting through this immunity is astronomically low.
Sources of Blizzard Damage Edit
For a basic Casting Cost of 200, this spell will deliver a Blizzard Damage attack against each and every enemy unit inside a targeted overland map tile. Each unit is struck with exactly 6 points of Blizzard Damage.
This spell is particularly useful against large enemy armies, since the more units present the more Blizzard Damage is delivered overall. It is even more powerful if the enemy army contains several Multi-Figure units, since these tend to suffer much more from Blizzard Damage than you'd normally expect. However, an attack of only 6 is fairly weak against Single-Figure units, and is unlikely to kill any of them, particularly heavily-armored ones. Ice Storm is often used to weaken an enemy army prior to actual battle.