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1.4.7. Buy back fallen heroes in battle (not to be confused with heroes who fled; you can "dig up" enemy heroes).
(The last two points are explained as follows:
1. It is forbidden to hire a dismissed hero on the day of dismissal. On any other day, it is possible.
2. It is possible to hire a hero who fled (or bought his way out) on the same day.
3. It is forbidden to re-hire your own fallen hero.
4. You can hire a fallen enemy hero at any time.)
I agree with points 1-3, but I disagree with point 4.
I don't know how it is for official tournaments, but for online tournaments, it introduces a significant imbalance in the game.
Let me give an example from my own experience. :)
Once, my friend and I were playing, and there was a moment when his main hero died, and when I went into the tavern and saw his hero... my friend said that this was a bug (hiring a killed hero, regardless of who he belonged to) and that it shouldn't be used. And I agreed with him, and we made it a rule not to hire killed heroes, or any already leveled-up heroes (hero level greater than 1), with one exception: if it was your hero and you fled/bought your way out with him.
P.S. It just occurred to me that this bug can also be used in offline mode... for example, by killing a companion hero, you can then dig him up with a hero-digger. This will give you an advantage, and it won't matter that the hero might not be leveled up exactly as you wanted, but nevertheless, it is.