The following are important game concepts not fully elucidated in the manual.
WEAKNESSES AND PROTECTIONS
Having a weakness means that a unit suffers 50% extra damage from the specified attack type. Having a protection means that a unit only takes 50% damage from the specified attack type. Having immunity means that unit suffers no damage and no negative effects from the specified attack type. Sounds simple, doesn't it? What makes the whole protection/weakness thing complicated is that is rare for attacks to come from only one attack type. For example, look at the description of 'holy bolts.' It inflicts holy AND fire damage. 'Black bolts' inflict death AND physical damage. Any unit with 'strike' inflicts physical damage, so the draconian flyer inflicts 'poison' AND 'physical' damage. How do protections and weaknesses work when there are multiple sources of damage?
The rule is this: a unit only gets the damage reduction from having a protection or immunity if it has protections/ immunities for ALL of attack types it is hit with, and a unit suffers from 150% extra damage if it has a weakness for ANY of the attack types it is hit with. For example, the witch has physical protection. If it is attacked with by an elven archer, it takes only half damage from the arrows because archery is a physical attack and the witch has physical protection. If the archer has enchant weapon, however, the witch will take full damage from the archery because now the archery has a physical and magic attack (enchant weapon affects range weapons.) She would now need magic protection also to take 50% less damage from the enchanted archer. A frostling shard thrower has fire weakness. A runemaster will always inflict 150% damage on the shard thrower because the runemaster has fire strike, and the shard thrower has fire weakness. It makes no difference that the runemaster strike is also physical, and the shard thrower does not have physical weakness.
What happens if a unit has both a protection and a weakness for a particular damage type? It will suffer 75% damage (the damage is reduced by half and then increased by 50% for 75%).
Notice that protections, though they reduce damage by half, do not help the saving throw for any effects that a special damage type may inflict. So having cold protection does not help the unit's chances of resisting being frozen. You can see that protections are less helpful than weaknesses are hurtful. That is why the frostlings got screwed- most of them have cold protection and fire weakness, which may seem to balance out in the end. But since weaknesses are much more harmful than protections are beneficial, they got a bad deal.
LIMITED RETALIATION STRIKES
This is an important concept to understand. Every unit (unless it has double-strike) gets four retaliation swings to use when defending in a combat round. Once the used these up, any further attackers will get free swings on the defender for the remainder of that combat round. This makes it possible for masses of lowly units to take out the most powerful units in the game. It also opens up many possibilities for creative play in tactical combat. Target the most powerful defenders with expendable melee units to drain their retaliation, and then use your own power-hitters to get free strikes on the defenders. Note that since combat strikes are tied to movement, each retaliation swing drains 1/4 of the defender's movement. So if you completely drain a defender's retaliation strikes, he will have no movement points during the next combat round (although he will get another four retaliation swings).
Thus, no unit in AoW2 is unstoppable. Even a hero with 20 stats all around and 30 hit points can be defeated by a big enough mob, because all that hero gets is four retaliation swings before he has to stand there helplessly. This is unlike AoW where the uber-hero could retaliate without limits. Note that if a unit has double-strike, it will get an extra swing, so it can effectively gets eight swings, although not eight different retaliation strikes.
Keep in mind that archers do not drain retaliation when they attack. So sometimes, if you have a unit like the charioteer which has a melee and archery attack, you may still want to use melee to drain the defender's movement rather than archery if you are setting the defender up to be attacked by another unit. It all depends on the situation.
THE POWER OF FLYING
If you frequent the forums, you've probably seen a ton of complaints about how flying is too powerful. That complaint is well deserved. Flying, of course, gives a lot of advantages on the strategic map: it grants a unit the ability to enter any terrain, go over lava unharmed, and cross over webs underground without being stuck. But its most unbalancing traits come out in tactical combat. Fliers can only be attacked by fliers. Non-fliers can only hurt them by defending against them in melee or using a range weapon. The other options are to bring them to the ground via web, entangle, lightning, or cold attacks, or directly attack them with wizard spells. This means fliers can pick and choose their ground opponents in tactical combat. Combined with the limited retaliation rule discussed above, this gives fliers a huge tactical advantage. Fliers with low hit points can wait until an enemy unit is drained of retaliation strikes, and then get free shots while being invulnerable to attack during the defender's round to move. This advantage is exarcebated the more fliers there are in a group.
For example, consider one manticore attacking one knight. The knight, although he can't attack the manticore, at least gets to strike back once the manticore engages in. Should be an even battle. Next, consider eight knights attacking eight knights. All the knights can be attacked by any of the opponents in any round, which makes for a fair fight. Now consider eight manticores fighting eight knights. The manticores can all gang up on a single knight per combat round. After two manticores attack, the defending knight's retaliation is completely drained and the other six manticores can attack with impunity. During the knights' turn to move, however, the knights can not similarly gang up on a single manticore because they cannot attack flying units. So they do nothing. The next round, the manticores gang up on the next poor knight. Any manticores that were hurt from the first round will be used last, so they can attack after the knight has used up all his retaliation strikes. Pretty soon, it will be four or five manticores against the last knight.
Flyers have other big advantages in TC. They can fly over walls, which makes them great city attackers. If you're ever attacked a city full of archers with a group of ground units, you know how tough sieges can be. Flyers can just go right over the walls. Conversely, when defending cities, they can literally obstruct the gate entrances, preventing ground units from coming in. If the attackers have no way to attack fliers or crush walls, there is nothing they can do. Four big fliers and an archer defending a city can kill an invading force of 20 knights. All the fliers have to do is block the gates while the archer picks off the knights from the city walls.
Given these advantages, it should be clear that if you have access to fliers you need to think about how you can start building them quickly. You also need to think about how you will deal with enemy fliers. More on this later.
If you've played any turn based strategy games before, you will probably understand the importance of turn advantage, or initiative. Turn advantage is how many turns ahead of your opponent you are in development. Think about the game as a big race between you and your opponent to gather all the resources, create troops, and capture key strategic points. Turn advantage is how far you are ahead of your opponent in this race. In chess, white starts with a turn advantage over black, because white moves first and can deploy his pieces one turn before black can. White can lose this turn advantage, however, if he makes mistakes and black forces him to waste moves.
AoW2 is much more complicated than chess, but the principle is the same- if you can build turn advantage and keep it, you will most likely win the game.
Even more important, the earlier you obtain turn advantage, the more it pays off in the end. For example, if you can get your first unit out two turns earlier than your opponent, your unit will basically have two extra turns to scout, gather resources, and conquer cities with that unit. All that extra stuff means gives you even more of a turn advantage later on, because you might have gotten your second city a turn earlier than your opponent, which means you'll have that much more gold and production earlier than your opponent. Your initial turn advantage snowballed into an even bigger one. When players of equal skill are playing against each other, a lot of times the game is decided quite early on by small advantages that snowballed into much bigger ones by the mid-game.
This is not to say that turn advantage cannot be overcome. Because there is a luck factor in AoW2, even the best advantages can be wiped out in a single battle. And there is plenty of time to correct mistakes later in the game. But you do not want to be in situation where you have to rely on luck or your opponent making a mistake to bail you out- so build and preserve turn advantage as much as you can. This means playing aggressive. I don't mean rushing to attack without a plan; or not building a solid defense; only that you simply cannot turtle against a good opponent in AoW2. You should always be trying to gain something every turn that builds your time advantage, and always look out for the opportunity to reduce your opponents' turn advantage.
DIVERSIFY YOUR FORCES
No, I am not a stock broker giving you advice. But from experience and frustration, I have to point out that using a single dimensional army is a recipe for disaster against a skilled opponent. When I first started playing, I would mainly use power level 3 forces, and just crank them out. This worked pretty well most of the time, but it sometimes ran into problems. A stack of warlords looks impressive, until you realize you have nothing that can attack fliers and an air galley can take them all out at once. Or that their resist is pretty low and a couple of incarnates will feast on them. However, if you put a few abominations with the warlords, you suddenly have a strike fhat is much more effective.
By diversifying I mean your army has to be diverse enough to be able to deal with the various situations that can come up. Can you deal with range attacks? With flyers? With special effects like 'dominate'? Can your army defend cities? Attack cities? Deal with magic bolts (priests are often used by good players en masse to defend their cities.)? Some units are blessed with a variety of abilities that can deal with all sorts of situations. For example, the charioteer is a powerful melee unit that has great speed and also a great range attack. There is little it can't deal with. Any flying unit already has a big advantage in this respect, since they are quite fast.
If you know what your opponent has, then great- you can construct a one-dimensional army to take advantage of her weaknesses. No use worrying about your warlords' low resist if you know your opponent is not going to have units with powerful special abilities. But most of the time you will not know what your opponent has, and you need to be prepared for anything. This is especially important in the starting selection process.
SIEGES AND ARCHERS
Archers in cities with walls are tough. Good players will almost always have lots of archers defending their cities. If you have a ground force, you might find it extremely frustrating to attack. I'll talk below more about laying siege to a city, but for right now you should realize that archers are especially strong in cities because of the elevation bonus. You should also realize that they are the best ways to defend cities, and that upon capturing a city you should almost always crank out a few archers for defense.