How do you create a powerful hero?

Properties of the desired hero on the map => double-click on him in the window that appears => in the "Skills" tab, enter level 40 (a higher level can only be obtained through a script/leveling up) and select the desired skills, naturally, of the 5th degree => then go to the "Bonuses" tab and enter the maximum possible values there. The bonus procedure can be repeated using a script.
If you want a simpler approach, just place a bunch of power-ups near the hero and let him collect them. Good luck ;)