The Black King is a highly sought after weekly boss, waiting in Fort Black: Panic Room.
Weapon: Sword of the Black King (High-Very High Slashing Damage)
Fighting the Black King requires important preparations beforehand. The best slashing-resistant gear available (95/40 minimum) and a very high damage piercing weapon (60+) are mandatory for the fight.
If all those prerequisites are fulfilled and you are lucky enough to get into a fight with the King, hope RNG is on your side. Due to the very high block chance and damage reduction of all the pieces of his gear, only high critical hits will dent him. The high block chance also typically makes for a very long fight, so don't neglect your block chance