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I would like to know more specifically about the deadline and the map name.
If the darkness is a major concern, download the "Dim" artifact. In principle, you can compensate with magic resistance, Barbarian luck, and magic disruption from goblins.
If there's no way to rush, take Attack + Leadership until Retribution.
Reflection is governed by great randomness; all questions should be directed to it.
As for heroes, try Hagash, Goshak, Arghat, and Garun.
However, if you drag it out until you have very large armies, it's quite difficult to defeat the Orc. Many Knights + Darkness (even if dimmed) usually do the trick. If the map allows, it's best to take Machines and attack as early as possible.