This article is extracted from a
post by Edi in the Game Play Strategies forum.
I don't remember if we had any post like this here in AoWH, so I dug up this post of mine from the Lifeline so we can add it here. This was originally an answer to a question on FC rules and how the AI prioritizes its resources and targets and how the order of engagement is determined.
This is how FC works as far as I know, but if I have forgotten something or gotten something wrong, please feel free to point it out. I have tried to present the information in as distilled and clear a form as possible without omitting anything, and I have tried to avoid paragraphs that need elaboration. I hope this helps.
I don't know if this qualifies for being one of those sticky threads or for the Strategy Tips section of AoWH, but if so, I'm happy to have been of help.
BTW, this is the 'off the top of my head' post Unicorn referred to some weeks back, if anyone remembers, though it's been edited a bit for additional clarity. The FC Tips section, for example, was not included in the original.
Wall breachers (battering ram, catapult, cannon, giant, beetle, bone horror) always go first. I have seen an exception to this once, and only once, and that battle included a hero who may or may not have had wall climbing.
Heroes with wall climbing do not use that ability to attack units inside walls if there is any unit with wall breaching included on their side. They wait for the wall breachers to either take the walls down or die first.
Ranged units go next. Long range units (ballista, catapult, cannon, ships, units with doom gaze) get in two shots before melee units get to them, except against cavalry whom they get to shoot only once before melee is joined. Archers get one shot against everything except cavalry before they are exposed to melee attacks. Even if units have high enough movement to close with archers before they can fire (36 or more), the archers go first unless it's cavalry they are facing. There are curious exceptions to this at random intervals.
Distance is not relevant. All armies start next to each other and start swinging.
Terrain obstacles do not exist. This even seems to apply to walls when attacking archers shoot at the defenders inside. Enemy melee units are still prevented from entering until the wall is breached.
Any unit can hit any unit unless impossible by virtue of movement type (ground vs. flying) or walls. A unit may be attacked by an unlimited number of units in the same turn.
Heroes always cast spells if they have channeling available. This can be prevented by starting to cast a spell that takes more than one turn to complete and canceling it after combat.
Heroes always use missile attacks to the exclusion of everything else, even if they have a much stronger melee attack.
Units with round attack will only hit one unit on the first attack, but then they will always (attempt to) hit at least three units if they use round attack.
Units with seduce/charm/dominate will use it to the exclusion of all other abilities whenever possible.
The AI uses healing to heal units even if they only have a single point of damage.
The AI seems to be unable to utilize Turn Undead in FC. For some reason I've never seen Turn Undead used, which makes is very annoying if you run into wraiths with a group of paladins or frostling shamans. Neither of those units has magic or holy strike and if they don't use Turn Undead on the wraiths in FC, they're screwed. I'm not sure if there are other powers the AI does not use in FC.
The AI always flags pure missile units (i.e. no retaliatory strike) as the primary targets and starts on melee units only after they are dead. In sieges, battering rams, catapults and other wall breachers are always targeted first. I'm not sure whether battering rams are moved to the last priority when they manage to breach a wall. I can't remember that one.
Comment by Thrashbarg: I understand that pure missile units target the strongest unit in the stack, missile unit or not. Melee units target pure missile units only if there is no badly damaged melee unit.
The AI tends to target the most powerful enemy units first (after missiles, that is), wasting hordes of units when it would be much more effective to concentrate on first taking out important low and medium level units and leaving the big baddies for the last. This makes fast combat especially frustrating, since even if you would lose in TC, you could at least inflict losses in proportion to your strength (or even completely out of proportion as the case may be) and possibly severely weaken the effectiveness of an enemy stack (e.g. by eliminating their wall breaching capabilities).
The AI is unable to distinguish which units pose the greatest threat to your army if wraiths or incarnates are present. The only shaman in the stack might shoot magic bolts at the flame thrower while the wraith wreaks havoc with the defenseless units. It will not do anything about it until higher priority units are dealt with. I'll be damned if I can understand that algorithm past the 'missile units' first approach, because it starts to lose consistency after that.
When faced with multiple target choices for archers, especially flying ones, the AI sometimes keeps switching targets and accomplishing nothing instead of killing one or two of the enemy which would otherwise happen.
Consequently, the rules of thumb:
1. Don't use FC
2. If you absolutely have to use FC, make sure it's overkill
3. Never ever use heroes in FC.
4. Again, if you have to, make sure they have zero channeling left or are casting a spell that takes more than they can channel that turn.
5. You can nearly always reach a better result in TC, but there are exceptions.
With this in mind, get familiar enough with FC that you can comfortably use it (e.g. with a small test map where you simply put stacks of various composition and pit them against each other until you have an idea of how it works. If you decide to play PBEM, all combats initiated by the AI against you and all combats between players are of necessity FC, all combat you initiate against the AI can be either TC or FC.
In conclusion, FC can be a powerful tool once you learn to use it and know what makes the AI tick. And still there will be surprises from time to time. It is, however, one of those double-edged swords that need to be wielded with great care lest the swordsman wound himself. Consider yourself warned.
Units with seduce, charm or dominate gain a very good advantage in FC, especially if used in groups. The AI will automatically have these units try to use these abilities as the main attack if it is possible. If you see an 8-stack of nymphs, ladies of pain, satyrs, doom priests or something else with one of these abilities, be afraid! Be very afraid! If it's a stack of incarnates, things are even worse...
If you've only got archers garrisoning a city and the enemy comes in with catapults, giants or cannons, use FC. That way your archers will get something done instead of getting killed when they rush out and are cut down by enemy melee troops. Of course, you can wait for wall breaching in TC and then sell yourself as dearly as possible, and this option is recommended if the enemy has a lot of archers/shamans/other non-wall breaching missile units, because all attacking units go first. Without the wall for protection (as per the FC mechanics), FC would be nothing but suicide.
Long range missile units (ballista, shredder bolt, catapult, giant, cannon, ships, air galley) in a group are well used in FC, because they will get two shots off before anyone reaches them when you are the defender, and at least one shot when you are the attacker, depending on what you attack.