Heroes 5.5 WarGame Edition - Tactical Edition.

Or will it be possible to implement it like this:
Avenger level 1 - one unit from each faction in the list of sworn enemies
Avenger level 2 - two units from each faction in the list of sworn enemies
Avenger level 3 - three units from each faction in the list of sworn enemies
Avenger level 4 - four units from each faction in the list of sworn enemies

The list is set during the hero description stage in the game's resources.

In theory, it can be assumed that this trick can be done using scripts, but it is a rather complex process.
The principle is as follows:
Four copies of the hero are created in the resources, with 1, 2, 3, and 4 enemies in the sworn enemies list.
At the start of the game, copy 1 is used.
When the hero reaches level 2, all parameters (stats, skills, spells, experience, army) are "read" from the hero.
The hero is replaced with its copy with 2 sworn enemies.
All the "read" parameters of copy 1 are given to him.
And so on.