Journey

What if you try to kill a Lawful Knight with Death Knights? They can destroy 25% of the enemy unit. There are plenty of them in the peaceful areas; hire heroes in the tavern and give them 5 knights each, after first leveling up the heroes with the "Fight to the Last" skill, and then go for it. Reduce his army and then kill him with the main hero. Plus, use the Mask of Justice! It's 100% possible to kill him, it just takes time, and is it worth it?))) Only if you're curious.

Added 1 minute later

It worked on summoned creatures, I was surprised. Although, maybe these are different.

Could Sandro's Cloak help with mind control?