The bonus of the Witch king lets them cause Fear in melee targets, which causes the target to run away for a short distance and prevents it from retaliating.
The Witch king is most likely to learn Nobility and Chaos magic and fairly likely to learn the Tactics, Combat and Death Magic skills. Witch kings cannot learn Life Magic or Order Magic when leveling up unless some basic training in those skills is already known.
The ability to drive creatures away with melee attacks can be very useful, particularly if the hero also casts First Strike on themselves - the enemy will take damage, then run away before it can retaliate. And when it tries to strike, the Witch king will be able to retaliate before its attack, causing it to run away again without attacking.
Be careful when facing more than one creature, or a creature immune to fear. Also, most ranged creatures will be even more dangerous, as they can run away from the Witch king when attacked, then strike from range for full damage.
|Heroes of Might and Magic IV classes|
|Standard hero classes||Knight - Death Knight - Lord - Thief - Archer - Barbarian - Priest - Necromancer - Mage - Sorcerer - Druid|
|Advanced classes||Archmage - Assassin - Bard - Battle mage - Beast lord - Beastmaster - Cardinal - Crusader - Dark Lord - Dark Priest - Demonologist - Enchanter - Field marshal - Fire diviner - Fireguard - General - Guildmaster - Heretic - Illusionist - Lich - Lord commander - Monk - Ninja - Paladin - Prophet - Pyromancer - Ranger - Reaver - Seer - Shadow mage - Summoner - Warden - Warlock - Warlord - Witch king - Wizard - Wizard King|