Heroes 6 - Discussion

By the way, could you tell me about the Duel mode? Can it only be played with a dynasty hero who has completed the campaign? Is it impossible to change the hero's class?

You can create a hero specifically for duels.
Go to your dynasty, to the section where your heroes are listed.
Click the plus sign and create an additional hero, choose their gender, appearance, warrior-mage class, tears or blood class, and click the checkmark to create them.
A level 30 hero will appear in your dynasty, then click on the skill icon under their avatar and spend 30 points to give them skills.

This hero will be weaker in terms of stats, compared to heroes from the campaigns, as they haven't gone through the upgrades, but they will be stronger in combat skills, because they are already level thirty and you can take the highest skills, which are only available after level fifteen.

Added 2 minutes later

It has nothing to do with the campaigns.

My dynasty heroes have the stats, skills, and spells that they had at the end of their final missions