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Try playing as a Warrior. At the beginning, it should be easier for him against a crowd of enemies, although that's not a certainty, as this is a custom map. I played custom maps for the first Heroes of Might and Magic, and not all of them were good.) You can also try playing as a Monk; he has a dodge ability. Increase his Agility and you're good to go.
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You can also run and shoot.