A hero from the Order Faction. Unlike other heroes from his city, he doesn't focus on magic itself, but rather on the army. And, to be more precise, on a summoned and animated army.
The first thing to pay attention to is his items. "Quiver" provides an endless supply of arrows – a signal that you should focus on archers (mages and titans/thunderbirds).
Secondly, the extra mana bonus for mages in the army (they have more mana and magical power) is given to us by the Sar-Issa Robe and Crown. Again, a signal – the emphasis is on the magic of the army, not the hero's own magic (don't forget about the bonus to knowledge and spell power. Also, the second "special" ability of these armor pieces will be very useful).
And lastly – the "Elemental Belt" and "Book of Power". Thanks to these artifacts, we have a bonus of both a general nature ("Book of Power" gives knowledge and spell power) and a specific one (bonus to summoning elementals).
Skills and Abilities
The first thing that catches the eye is "Fog Cloud" and "Evasion". Two abilities that effectively undermine the archers in the enemy's army.
Next, pay attention to the "Sharp Mind" ability. In combination with the Sar-Issa artifacts, they work well together – we move the hero faster both at the beginning and later, during the battle.
"Unraveling" is, in principle, a good ability, but in this context, it is completely useless. We already cast summoning magic well.
"Master of the Earth" gives a bonus to fire traps (we don't need earthquake). More on the plus side of this ability later.
"Lord of Magic". Looking at this ability, we are reminded of elementals again. And not only. Phoenix will also be of great use to us.
We have a hero with a strong focus on archers and mages.
But this means only one thing – we will have to play defensively. A strong defense. We will be helped in this by the good weakening of enemy archers, as well as summoning magic. Even more summoning magic...
That's the thing. Phoenix flies around the entire field, but you can't lead it into attack – the defense is weak. Only 45 gargoyles! Therefore, in defense, Phoenix and... Rakshasa sit. Elements and (!) fire traps help them with this. Titans/thunderbirds do not need defense – they are a good defense in themselves.
But here's the problem – your mages are killed. There is nothing to fight with... but we have "Raise Dead"! 22 mages at a time – is that a joke!
That's basically it.
Jallib has a strong defense, powerful magic/archers. At the same time, his opponents shoot poorly themselves...
The question arises – how to deal with this? The answer is simple!
It should be remembered that our enemy has powerful summoning magic. And a phoenix. Therefore, you should take a hero who neutralizes this advantage (for example, Ayres).
Another way is to take a hero who can easily break through the enemy's defense. This is either the numerous army of Anwen, or the imbalanced army of Nimue, or the tank-like army of Helmar.
You can try not to break through the defense, but to cast spells on the enemy army. This means that you need a hero with strong magic – Ravenna, Synitar.
You can try to "freeze" the enemy with Orson.
That's basically it. The rest of the heroes are either ineffective or completely ineffective (for example, the attacking horde army is unable to break through Jallib's defense).
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Here is a "mini anti-guide". Please love and cherish it (=
P.S. I'm rereading it and thinking – I wrote so much for the last three paragraphs! O_o

"Смерть - лучше опозоренной чести"