It's very simple:
Heroes like Jelu, Dragon, etc., create an imbalance in the game. If you want to play on a specific map with a specific hero, just open the map in the editor, press Alt+Enter, and in the hero menu, check the box next to the portrait of the desired hero. Then, save the changes, launch the hero, choose the map, and play. :)
I think you need to press Ctrl+Enter.
But there's an even simpler way - drag the desired hero to your castle in the editor, save the map, and then play on it... Otherwise, even if the editor allows you to obtain the desired hero on the map, there's a low probability that he will appear in the tavern... :)
