In the unmodified game, this ability is exclusive to a single creature: the Sky Drake. It is not possessed by any other unit, nor can it be added to them by any means. As such, this article focuses almost entirely on the ability of this creature. In a modded game, Lightning Breath will likely behave exactly like Fire Breath with 3 exceptions: its damage is not subject to Fire Immunity, but is instead Armor Piercing; and the Attack Strength might be enhanced by different Node Auras (based on the type of the unit that has this ability).
The strength of the Lightning Breath ability possessed by the Sky Drake is 20, as is indicated after its name in the unit statistics window (where it is denoted simply as "Lightning", i.e. Lightning 20). This shows the maximum amount of Damage that it can cause, though the attack itself is subjected to To Hit rolls and the target's Defense rolls as is usual for most types of Physical Damage.
The Sky Drake possesses a unique ability that allows it to literally breathe out lightning bolts. These are concentrated towards a specific target, and can cause significant amounts of damage. Due to the nature of lightning, armor can do very little to stop it. Units attacked by Lightning Breath can, at best, try to dodge out of the way. A direct hit by this concentration of electricity is deadly to the vast majority of units.
Lightning Breath is automatically used whenever the unit voluntarily makes a Melee Attack against any opponent. It is not available during Counter Attacks, but it does allow the Sky Drake to engage Flying opponents even if it is grounded by a Web spell.
As a Breath Attack, Lightning Breath is executed before any other attacks or exchange of damage between the Sky Drake and its target: it precedes any Gaze- or Touch Attacks that the opponent might have, and occurs well before the delivery of Melee Damage by either combatant. In fact, any opposing figure that is killed by the Lightning Breath will never be able to deliver any of those attacks or damage. This gives the Sky Drake significant protection from enemy units so long as it can maintain the initiative and not let the opponents attack it first.
Lightning Breath is carried out in a similar fashion to a regular attack. An Attack Roll is made using the strength of the ability (usually 20 or 22) to determine the raw damage that can then be mitigated by the target's Armor. However, Lightning Breath also deals Armor Piercing Damage, which means that the opponent's Defense score (apart from any immunities, more on this below) gets halved for the purpose of making its Defense Roll(s).
Lightning Breath is considered to be Magical Damage, in addition to actually being associated with the Chaos realm. This has some negative consequences in terms of it being defended against. Magic Immunity and Righteousness both increase a target's Defense to 50 against this Breath Attack, and both of these effects also override the Armor Piercing Damage component, making units possessing either of these very resilient against Lightning Breath. City Walls, if in play, also ignore the Defense-halving effect.
On the other hand, all other conditional modifiers do get cut in half, which is a good thing as most of them do apply against this attack. That includes the Large Shield ability (halved to +1), and all 3 protective Unit Enchantments that increase their target's Defense based on the nature of the incoming attack: Bless ( +3/2), Resist Elements ( +3/2), and Elemental Armor ( +5). Since the first two of these spells grant an odd bonus, it's halved value depends on their target's original Defense.
Units with Default Lightning Breath Edit
There is exactly one unit in the game that possesses Lightning Breath:
Sky Drake - Lightning Breath 20
With a Lightning Breath strength of 20, the Sky Drake delivers an extremely powerful attack that can kill enemy units before they get any chance to retaliate. Given the Armor Piercing Damage caused by the attack, even heavily-armored units are at risk from it.
Acquiring Lightning Breath Edit
There is no known method of adding a Lightning Breath ability to any unit that does not already possess it.
Improving or Hindering Lightning Breath Edit
There are only two effects in the game that have a direct positive effect on Lightning Breath: the Sorcery Node Aura, and the (High) Prayer spell. Similarly, there are also only two effects that can directly reduce its effectiveness: Black Prayer, and Warp Reality. The main reasons for this scarcity are the facts that the Sky Drake is a Fantastic Creature, excluding it from many positive effects; and it is also innately immune to both illusions and magic, making it impervious to all single-target negative modifiers.
Attack Strength Edit
In terms of Attack Strength, entering into any battle that takes place in the area of influence of a Sorcery Node improves the strength of Lightning Breath by +2 for all Sky Drakes present, regardless of whether they are friendly or hostile. Black Prayer, on the other hand, only penalizes units hostile to its caster, reducing each of their Attack Strengths by 1, including a -1 to Lightning Breath.
Chance To Hit Edit
As for modifiers To Hit, casting Prayer or High Prayer will benefit any Sky Drake on the caster's side, granting an extra +10% chance for each point of Lightning Breath Attack Strength to score a successful hit. This bonus can only be applied once, casting both spells simultaneously will simply make one of them redundant.
Finally, Warp Reality is another battlefield-wide effect that penalizes friend and foe alike. That is, unless they are associated with the Chaos realm, which the Sky Drake is not. This effect reduces the chance To Hit of all affected units by -20%, and applies to all of their attacks, even if the attack itself is actually associated with Chaos (as is the case with Lightning Breath). This makes each point of Attack Strength 20% less likely to be able to cause any damage.
Other Effects Edit
There are also a few other spells that have some influence over the Breath Attack granted by this ability. Haste will cause Lightning Breath to be executed twice in a row during the Melee Attack sequence, while Immolation will also add its strength 4 Area Damage attack on top of it, unless the game is played using the Unofficial Patch 1.50. In addition, Invulnerability, particularly when enchanted onto Multi-Figure units, may seem stronger than normal against Lightning Breath, as its damage reduction of 2 completely ignores Armor Piercing Damage. This is also true for Blur, although the effect of this spell is not overly noticeable to begin with.