I conceived this section quite a long time ago. But only now did I realize that the original title "Reinforcing a Knight army in computer castles" does not fully reflect the issue, since one of the main resources for reinforcing a Knight army is capturing Draco-grad and purchasing red dragons there. This move is quite obvious, so let's now move on to considering the possible reinforcement of a Knight army in computer castles.
So, after capturing a castle, we have 3-4 squads; among them, there are likely 3 quite sturdy ones (pikemen, swordsmen, champions, paladins - most likely 3 squads from this list) plus a somewhat diminished squad of shooters.
One feels the desire to add someone.
Let's reflect on this topic for a bit.
Intuitively, we understand that, for example, taking 18 skeletons into this army is unnecessary. Let's try to figure out why intuition unerringly told us this and if there are any general rules regarding this.
Right now, our morale is +4. General rule: without visiting special objects, morale +3 is the most useful in battle, and +4 in the case of a battle with bone dragons. But we probably won't specifically plan for a battle with bone dragons, so we will strive for morale +3. And adding undead immediately reduces our morale by 2 points, down to +2. There have been attempts to calculate how much 1 morale "costs" in an army, but for now, we will not touch upon that and will approach the question from another side.
What are our strengths? These are infantry units, power stats, morale, and a fairly fast army.
What are our weaknesses? Magic vulnerability, lack of flying units, and quickly dwindling shooters.
Now we understand why taking 18 skeletons is probably unnecessary: they lower morale, while adding neither flyers nor shooters.
Therefore, when evaluating possible reinforcements, we will rely specifically on these factors.
Now let's try to formulate a general hypothesis (which does not claim precision, but only provides general guidelines).
We will consider the possibility of adding a squad from another castle in the following cases:
-) for infantry: if the squad's strength is at least 20% of our army's strength (for Necromancers - at least 30%);
-) for shooters: if the squad's strength is at least 10% of our army's strength (for Necromancers - at least 15%);
-) for flyers: if the squad's strength is at least 10% of our army's strength (for Necromancers - at least 15%).
At the same time, we take into account the squad's speed. It should also be kept in mind that it may be more important to preserve the ability to merge/tactically reposition by having 4 squads instead of 5, than to increase the army's strength by adding 5 minotaurs (rocs, vampires) or 4 unicorns (mages, liches). And in most cases, it only makes sense to add units of level 5-6 to the army at the cost of reducing morale.
1. Necromancer castle. The main feature is that upon reinforcement, morale drops immediately by 2 units. Skeletons and zombies are not considered. Mummies. Only if upgraded, and even then, not very desirable. How many could there be? Maximum scenario: capturing the castle on day 7, placing mummies, upgrading and buying them out on the first day. That would be 10 units. But more likely it will be 6 units, because building and upgrading mummies without the goal of further developing the castle is unlikely to be profitable. That is, according to our hypothesis, we probably won't take mummies either. Vampires. Better if they are lords. They can be taken for the next 1-2 battles (as well as liches), simply to block enemy shooters, but we will not consider them as a full-fledged squad.
Bone dragons. 4 bone dragons are a fairly serious force, and they also lower the opponent's morale by 1. In general, they can be taken.
2. Barbarian castle. Here we can only talk about the last two levels. They can be taken.
3. Phoenix castle. The best candidates are the phoenixes themselves. It makes sense to take them; morale will hardly change, but you gain the possibility of the first move, a unit with partial magic immunity, and the possibility of "acceleration" (when spending the night in the castle, we station all units in the castle except the phoenix and champions; in the morning, we take everyone back and proceed with full mana and a long move). Shooters of level 3-4 can be taken only as a means of reducing losses for the rest of the army in the next few battles (like fairies). It makes sense to take unicorns in sufficient numbers (according to our hypothesis).
4. Titanic castle. This is where it gets most interesting. When playing on "impossible" level, one can often find unbought titans!! Of course, we buy them! It makes sense to buy rocs if there are archers in the army (since they have the same speed of 4); mages/archmages can be bought, although they will die quickly.
5. Black Dragon castle. Well, buying the dragons themselves is always interesting, that's obvious. We won't buy hydras because of their low speed. Minotaurs depending on their number and the strength of our army (according to our hypothesis). Griffins - similar to rocs in the titanic castle.
But! A magnificent unit dwells in this castle - the gargoyle!! And I strongly recommend (despite the unit's modest level) seriously considering the possibility of adding gargoyles to your army. They will block shooters, distract the opponent's forces, reduce the losses of the main troops, and finally, if necessary, allow you to equip a purchased hero with them so that he runs fast and captures mines.
Of course, much more could be told about amateur play with the Castle faction. But the longer we play on the map, the less the initial racial differences of the hero and the army matter.
I hope some of my tips will be useful, or at least were interesting to read!
Thank you for your attention,
Qwerty
A continuation may follow, but on a different topic...

Орден Феникса – харизматический :) лидер