The Witch-King of Angmar is Sauron's chief lieutenant and the Black Captain of the Ringwraiths. Once a great Númenórean king, he is now a phantom of malice bound to the will Sauron. In Edain Mod he is recruited from the Minas Morgul Outpost expansion at the cost of 2000; there you shall gain a veiled Witch-King much like the other Nazgûl. When "His Deadliest Servants" is unlocked, he will be able to unveil his identity as the Lord of Minas Morgul.
Level 1: Dread Visage: This ability lowers nearby enemy units' damage and armor by 10% and cancels all their eadership bonuses. Enemy heroes also lose 15% damage and armor. For every Nazgûl nearby the effect is amplified by an additional 5%. Additionally, he grants nearby Nazgûl an increase of 20% in movement speed, 50% in vision range, and 25% damage. (Passive ability)
Level 7: Morgul Corruption: The Nazgûl stabs the targeted enemy with a Morgul blade, poisoning them over time. If the unit dies while the effect is active, they will become a Lesser Wraith, which is invisible to enemies but has no attack. This will also cripple the target
His Deadliest Servants: Lordship of Minas Morgul: The Nazgûl is allowed to claim lordship of Minas Morgul. He gains the ability to ride on his fell beast, improved combat stats, a fearful mask, and a new set of abilities, fit for his rank. If he falls in combat, this upgrade will need to be repurchased. (cost: 1500)
Level 1: Mount/Fell Beast/Dismount: This allow the Nazgûl to Mount/dismount his dark horse and his fell beast. While unveiled, mounting his black steed changes the Witch-King's armor set to EdainNazgulArmorMountedUpgrade
Level 1: Visage of the Witch-King: This ability lowers nearby enemy units' damage and armor by 10% and cancels all their eadership bonuses. Enemy heroes also lose 15% damage and armor. For every Nazgûl nearby the effect is amplified by an additional 5%. Additionally, he grants nearby Nazgûl an increase of 20% in movement speed, 50% in vision range, and 25% damage. (Passive ability)
Level 4: Wraith Form (dismounted only): The Nazgûl casts off his robes and enters the spirit world. He cannot attack and cannot be attacked and can only cast Terrible Malice. He does retain his Dread Visage ability.
Level 5: Screech (mounted, fellbeast only): The Nazgûl screeches and sends his enemies fleeing in fear.
Level 10: Hour of the Witch-King (dismounted only): The Lord of Minas Morgul raises his sword and sets it aflame. This fires a shock-wave which causes damage and knocks back all enemies. For a short while he also gains a boost in attack damage and attack speed.
The Witch King can be given the following upgrade:
Insignia of Minas Morgul - The Witch-King gains new abilities, a new skin and a fell beast to ride upon. Changes his armor set to EdainNazgulArmorUpgrade. Cost: 1000.
In short, the Witch King is Mordor's best hero killer: his Morgul Corruption (before purchasing the Insignia of Minas Morgul upgrade) poisons the enemy, inflicting damage over time, and his Terrible Malice renders all heroes' abilities useless. Once the enemy is crippled and poisoned it is vital to use Hour of the Witch King, which offsets the enemy and grants a major single unit damage boost to the Witch-King. If things get hard you can use Wraith Form for a getaway with the possibility of cursing an enemy hero one last time just before running away. The Witch King, however, also deals equal damage to any ally troops in his way whenever he attacks, so it is best to keep him solitary or with other Nazgûl so that he can wreak havoc on the enemy. He can always flee on his fellbeast if things get difficult. While mounted he cannot make use of his flail, similarly to when he uses Hour of the Witch-King but in the latter he gains a huge damage boost to compensate, making him an effective hero killer for that time.