Discussion about Sylvan (Wood Elves).

I said that Prismatic Breath is unpredictable. Even if you have a Luck of 10, there is always a chance that it won't work...

I understand where the misunderstanding lies :)
I didn't think I needed to explain how the ability actually works :)

Quote from the manual:
Prismatic Breath
This creature attacks all targets within a random radius in a given direction.
“Prismatic Breath” hits from 1 to 5 cells in a random direction behind the target.
The number of cells hit depends on the creature's luck: 1+(random(1;10)+Luck)/2, with
rounding down and no more than five.

Do you see the formula?
Let's assume that the worst-case scenario happened and random(1;10) turned out to be 1.
Let's say we want to get a result of at least 5 cells.
1+(1+luck)/2 = 5
From this, we get: luck = 7.
That is, if our dragons have a luck of 7 or more, then their attack will, in any case, be 100% for 5 cells.
Only the direction of the attack remains random.

Now regarding the direction:
From the manual, we take the diagram of possible attack directions and see that the attack cannot go straight for more than three cells. It will definitely turn left or right.
The next piece of the puzzle :) The initiative of the dragons will allow them to go first, and their speed will allow them to fly directly to the enemy.
Next...
The enemy will place stacks tightly, in a line, as they use different troops.
Conclusion: if you have 7 luck or more, then when attacking with Prismatic Breath perpendicular to the line of enemy troops, the Prismatic Breath will almost certainly hit several stacks.
The attack will be for 5 cells in this case.

As for the usefulness of Prismatic Breath compared to the Warlock's dragons and their relative survivability.

Warlock's dragons - for the Warlock, Prismatic Breath - for the Wood Elf.
Therefore, Prismatic Breath will have much higher defense, and it is very likely that there will be a defense skill for the hero.
The Warlock's dragons will have less defense, and the hero will most likely not have a defense skill.
That is, Prismatic Breath will be much more durable.

Furthermore: Prismatic Breath will attack first, deal huge damage, and take the brunt of the retaliation, which will save weaker units.
Prismatic Breath will attract a lot of attention, as it is a very strong attack stack, which will provide cover for the Dryads, Dancers, and Archers, who are all very strong attack stacks, but at the same time very easily killed.
Prismatic Breath, due to its ability, is a more dangerous attack stack than Imps.

This is not observed in the case of the Warlock and dragons.
Here, the main striking force is the Warlock hero himself.
Among the units, the Warlock has only one attack stack with low survivability, similar to the Elf - these are the Furies. There is almost nothing to cover them with, as with the Elf.
And the dragon itself will not attract as much attention; it attacks quite rarely. Red dragons can only use their ability usefully with an attack teleport, which will cost the hero a turn.
And it is not as durable under the Warlock as the dragons are for the Elf.