Battle magic can only be cast during a tactical battle. These spells have battle effects like inflicting damage, granting increased protection, reducing fatigue, or some similar effect which only makes sense in the context of the battle mechanics. Battle magic can be scripted into a mage’s list of battle actions using Set battle orders. If a battle spell requires gems, that mage must have those gems in his inventory before the battle begins.
Some battle spells affect the whole battlefield and are termed battle enchantments. Some of these last the length of the battle. A battle enchantment is dispelled if its caster dies.
In combat, gems may do one of three things:
A mage may not spend more gems in one turn than his level in the relevant path.
For instance, consider the Alteration 5 spell, which requires an Earth 3 caster and 1 earth gem. An Earth 1 mage can't cast this spell at all. An Earth 2 mage can cast it by spending two gems; one to boost to Earth 3, and another for the spell's requirement.
The casting time detailed as a percentage of a round in the description of a spell is divided into two steps: the first half is spent by the mage preparing to cast the spell, the second half is spent recovering from the casting. The spell itself resolves somewhere in the middle, at half the casting time of the spell.
Of note is the fact that a spell does not resolve exactly at half its casting time. Instead, some randomness seems to be involved: a spell will resolves at half its casting time plus or minus a few ticks, the smaller division of time in a battle. This can be mechanically important, such as in the interaction between and . Let's assume we set up one mage to cast with his first script slot, and a group of A2 mages to cast then . We get the following result: among the A2 mages, some will start their second spell right before storm is up, i.e. before receiving the air boost, and thus will cast another spell instead as they do not meet the requirement for , and some will cast their second spell right after storm is up, and thus will be able to cast .
Some monsters are innate spellcasters. These monsters do not require any preparation time for their spells and ignore casting times.
During the preparation time mentioned in the previous section, the caster can be interrupted if he is damaged.
The chance of being interrupted when damaged while casting a spell is expressed as a percentage of your full hit points caused by the damage, plus 25%. Thus, a strike that inflicted half of a spell caster’s full hit points in damage would have a 75% chance of interrupting the spell being cast.
The method for resolving battle magic is very similar to that for missile weapons. Mages have a precision attribute just like archers do. Spells have a Precision rating, also. For the purposes of calculation these two are added together. Many spells have 100 Precision, intended to make them impossible to miss; unlike with Morale on Mindless units, however, this is not an arbitrary figure, and these spells can still miss if the target is too fast and moves at just the right moment. Some spells (like ) are armor piercing. This means Protection against them only counts for half, just like armor piercing missiles. Some other spells (like ) are armor negating. Other spells require their caster to make a successful magic resistance check in order for some or all effects to apply.
Spell range is measured in squares. Diagonals have a movement cost of 1.5 tiles.
Just like attacking in combat, casting spells in battle incurs fatigue. Each spell has a listed fatigue cost which a caster incurs when casting that spell. For each skill level in the required path that the mage exceeds the minimum, he incurs 1 / (1 + (mage skill – minimum skill) of the listed spell fatigue. In other words, having an extra skill level means the mage suffers only ½ fatigue, two extra skill levels means he suffers only 1/3 as much, three extra is ¼, and so forth.
Spell casters also incur fatigue equal to their base Encumbrance value + 2x Encumbrance value of any armor worn for each spell cast. This is not subject to reduction by skill bonuses. It is harder to make magical gestures in heavy armor. Fatigue is very important for spell casters. It is often the limiting factor in combat, and higher-skill mages thus have an advantage in that they incur less fatigue. Spells that reduce fatigue, like, and , can be very useful as well.