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I replayed the orc battle recently with minimal stats and equipment, and casting Entangle straight away outside the gate before they cast it inside the gate, helps very very much. Burning hands also helps. The orc leader is tough to take out.
The battle involves a good bit of luck as it depends on how long the friendly knights hold their own versus the orcs and gnolls.
Also, if they start casting Darkness, it's a bad omen for the outcome.