Walkthroughs for custom maps.

Well, you know... Standard maps, compared to custom maps, are like an alphabet compared to some novel. To say that you've missed out on a lot would be an understatement. Even to create your own maps, it's highly desirable to play on custom maps to see what original tricks, obstacles, and other challenges they have. These maps truly reveal the deep potential that exists in "Heroes."
Based on your description, I can't understand which map you're talking about, but I probably haven't played it: I don't remember such a victory condition; everywhere, it required defeating all opponents.