The crossbow adds no damage — it only lifts the one-Attack-per-turn cap, so its value scales with how many Attacks you are holding, not the card itself. It shines for aggressive heroes with a fat hand, or Rebels ganging the Lord to finish him in one turn. A Lord can use it to burn down a Rebel or Traitor before he gets swarmed back. Draw it on an empty hand and it does nothing.
Pair it with heroes who convert other cards into Attacks: กวนอู (Guan Yu) turns every red card into a machine-gun burst, and จูล่ง (Zhao Yun) swaps Defense into Attack to empty his whole hand at once. Extend your reach with ม้าเฉียว (Ma Chao) or the horse กระต่ายแดง (Red Hare) to hit far seats. Note: เตียวหุย (Zhang Fei) already attacks without limit, so the crossbow is wasted on him.
Since the volley is all basic Attacks, hoard several ป้องกัน (Defense) — one dodge per shot. แปดเหลี่ยม (Eight Trigrams) armor is even better, rolling its own dodge on every incoming Attack, which blunts rapid fire far more than a single Defense. Best of all, strip the weapon with ทำลาย (Dismantle) or ปล้น (Steal) before their turn to reset the cap. Do not count on ปัดป้อง (Negate) — it stops tricks, not Attacks.