Arrow towers are special addition to combat when hero is trying to capture a garrisoned town. A town can have a primary Arrow tower (when Citadel is built) or one primary and 2 secondary Arrow towers (when Castle is built).
Arrow tower damage depends on the number of "structures" - buildings built in a town. Not all buildings affect the Arrow tower damage, among them:
- All upgrades of Creature Dwellings, Mage Guild and Town Hall.
- Horde Buildings ( except Vault of Ashes).
- Citadel and Castle, since they are Fort upgrades.
- A few towns have several Specific buildings which are upgrades of the other buildings (e.g. Brotherhood of the Sword, Fountain of Fortune)
The damage of the primary Arrow tower is calculated by the formula:
Damage = Base_Damage + d * N
The damage of the secondary Arrow tower is calculated by the formula:
Damage = Base_Damage + d * N/2
where Base_Damage - is the base Arrow tower damage, equal to 10..20 points of damage for the primary and 6..12 points for the secondary Arrow towers; d - additional damage for every structure built, equal to 2..4 points; N - number of structures built. The result of N/2 is rounded down.
As indicated above, different towns have a different number of structures available, therefore, a different maximal Arrow tower damage range.
The Arrow tower damage cannot be changed by any other damage modificator. The Defense parameter of their targets is always ignored. Despite the right-click tip says that an Arrow tower has 10 Attack, final damage remains unmodified. Archery or the Artillery secondary skills do not affect the damage as well, but a defending hero with Artillery skill is able to control the Arrow towers during a siege. Arrow towers cannot deliver a lucky strike.
The only exception is a bug, which cause the troops under command of a hero with Armorer secondary skill take additional damage from the Arrow tower attack. Troops, which are buffed by Air Shield spell or are petrified take additional damage as well.
Arrow towers under the AI control
General observation: Arrow towers target the enemy troops depending on their "class". The class is assigned for every enemy troop stack based on their opportunities to deliver damage to the defending troops.
- Class A - the enemy troop stack can attack immediately when it is its turn to act. Ranged units, that still can shoot, belong here.
- Class B - enemy troop stack, which can't attack immediately, but can attack its next turn.
- Class C - enemy troop stack, which can't attack immediately and its next turn, but can attack after.
The AI considers the Arrow tower damage equal to 1 (bug), that is why it prefers to target the stacks with 1 unit in it over the stack of the same units with number, let's say, 10 in it.
There are 2 factors, based on which AI chooses its target. The priority target is calculated separately for each class.
Loss in army power
- For class A: priority = 1 * (AI Value / hp) * 100%, where 1 is the Arrow tower damage (bug); AI Value - total Value of the stack; hp - total Health of the stack.
- For class B: priority = 1 * (AI Value / hp) * 50%
- For class C: priority = 1 * (AI Value / hp) * 33%
Loss in army quantity
- For class A: priority = 1 / hp * 100%, where 1 is the Arrow tower damage (bug); hp - total Health of the stack.
- For class B: priority = 1 / hp * 50%
- For class C: priority = 1 / hp * 33%
After the calculations AI chooses a target with the highest calculated priority. If there are several troops with the equal priority, then the AI will choose a stack, which was placed in the rightmost slot of the hero's army.
Knowing this and considering the fact that the AI prefers to target shooters, it might be a good decision to fill your empty rightmost slots with ranged troops with a single unit in each of them. The other possible way of saving the friendly ranged stacks is to move forward, closer to the primary Arrow tower, a powerful stack of tier 1 troops or a flying stack.
Each faction's arrow towers will appear to be garrisoned by a different creature, typically the lowest-level Ranged creature available to that town (with a few exceptions). This is purely cosmetic, and the towers do not inherent any of the effects from their base creatures; for example, Necropolis towers do not have a Death Cloud effect despite appearing to be garrisoned by Liches.
Here is a list of each creature that appears in Arrow towers:
Damage calculation was changed to make Arrow towers more dangerous. Their innate 10 Attack points now added together with the defending hero Attack skill and increase damage properly, while still ignoring the target's Defense parameter. Archery now increase the Arrow tower damage as well. The Armorer, Air Shield and Petrification bug has been fixed, so these modificators now properly decrease the Arrow tower damage.