Playing as the Legions (Disciples 2).

You can explain this to the AI. It sees – oh, there's an archer in the front row, it definitely needs to be targeted.

The AI attacks those with lower HP! And even if the attacked unit receives healing, it will still attack it. The AI only switches to attack another unit if it can finish it off – no other way! It's a sin not to know this!
Some people wrote that succubi are useless – that's not true! The uniqueness of witches and succubi lies in the fact that after transformation, the enemy unit loses all its unique abilities, sorry for the tautology! A spirit, death knight, essence, or werewolf will lose their immunities, and armored units will lose their armor. Besides, it's much easier and faster to level up with witches (think of them as an analogue to ghosts for the undead). The only downside of a succubus is that the transformed unit returns to its normal state before its turn. That is, for example, a dragon will return to its form and make its move.
As for the incubus, its strength lies in the fact that it has a very high chance of success. Yes, on the screen in the game, we see the hit percentage – 65%, but that's not the case. In reality, it's higher, and based on my own experience, I can assume that the incubus has a hit percentage of around 75%.

Now, a few words about tactics for the Legions.
As mentioned above, the tactics depend on the map – this is only partially true.
The first thing you should do with the Legions is to learn the phantom spells and the summon Cerberus spell, and then intensively scout and explore the map. Knowledge is power!
Secondly, I want to emphasize the gargoyle. Believe me, this unit should be in your army in at least 80% of cases. First, it's the only ranged unit for the Legions; second, the gargoyle's resilience is colossal: immunity to poison (hello elves and orcs), mind shield (hello orcs – for now), and armor; third, it's an elemental type unit (hello lovers of invulnerability!).
The third aspect of playing as the Legions is the third-level spell, His Majesty – Invisibility! The spell is very cheap, both in terms of learning and cost. Invisibility is what makes the Legions truly what they are – cunning, ruthless, elusive(!)
I consider the Advisor to be the best hero for the Legions – a good amount of HP, a ranged attacker, high initiative, and, most importantly, the ability to fly. The Advisor, possessing the flight skill (a hero's unique ability), a large movement range, and also being under Invisibility, allows you to always be in the right place at the right time, to the envy and annoyance of the enemy. You don't even need to have a lot of potions, buff yourself, or perform a ritual dance... All you need is to be nearby and, at the right time, set up an ambush with consequences. :)

Sincerely!