War machines in Heroes V.

The catapult, even the improved one, doesn't always do what you want it to. It's better to spend a turn with the hero and immediately destroy the walls and gates, rather than waiting three times for a miracle from the catapult, i.e., that it won't shoot at the already destroyed part of the wall or tower. With archers and liches, I can overwhelm the mages easily, and gremlins are not a problem either, especially with their "killing power" and "initiative." After that, I'll hypnotize the djinn, rakshasa, or, if there are titans, I'll defeat the enemies with my own units. That's roughly how I do it, with possible variations.