They are summoned by their respective power, a Thrall Master (Special Missions), and by killing units with a Morgul-blade/Morgul corruption or the Well of Souls. They are not overly powerful or have much health, but they can heal themselves when killing units based on the damage. They can also gain the Black Mask passive debuff upon gaining enough experience, which reduces any hostile infantries attack and defense by 25%. They wield giant two-handed swords and have larger health pools than the Uruk-hai and dwarven infantry.
The Angmar faction can be thought of as the evil counterpart to Dwarven faction The Battle for Middle-earth II they are strong and sturdy, but slow. In the campaign, the player must dominate the land of Angmar, gather a huge army, and then launch a massive invasion that will span half a millennium in Middle-earth's history. The Rise of the Witch-king tells the story of the evil Witch-king’s rise to power, domination of Angmar and invasion of the great kingdom of Arnor. After the Great Plague in 1636 which devastates Gondor and desolates many parts of Eriador, the southern part of Arnor, the Witch-king finally destroys Fornost, and takes it as his own fortress. The tower of Amon Sûl is destroyed, but the great fortress of Fornost is defended, and war continues. The Witch-king settled in Angmar, and after having built an army there, invades Arnor in the year 1409, and waged a 500-year war against the kingdom of Arnor, the north-kingdom of Men. In the year 1300 of the Third Age, evil things started to stir in Middle-Earth again, and the Nazgul re-appeared. After a thousand years of peace that followed the War of the Last Alliance, evil once more began to spread across Middle-earth.