Ice and Fire

First, you need to kill the hero with minimal losses.
I have 20 devils, 49 cave goblins, 88 horses, etc.
The computer has 70 dragons, 105 jarls (who have a wave of flames), etc.
After that, take a garrison of 2 castles, each with 95 jarls (with chain lightning), a legion of guardians, etc., in the same spirit.
And then capture the castle, where Brand runs around with a group of dragons and a darkness of guardians.

Accumulating troops is not an option. The computer accumulated 70 dragons in less than 2 months, not counting Brand and who knows who else. You can't outdo that.