Has anyone played through Len’s mission in Heroes of Might and Magic II?

I haven't had a situation where I had three stacks of forty units at once. All heroes are different. But the main problem isn't even withstanding the initial onslaught. I could manage that by staying in my castle. The main problem is with the advanced magic of the Necromancers. They immediately have the Cold Snap spell at the beginning of the game. By the time I reach their Stronghold, I barely have an army left. In this regard, the Dwarves are good; magic doesn't always affect them.