Very hard creature to hunt, forget your Icicle and your Stalagmite runes here, since he is immune to Earth and Ice Damage. Since they are resistant to all other elements, all you can do is hit it with whichever attack you have, or use Explosions. It is not recommended to enchant your weapon to a hunt, since it isn't really necessary. A basic strategy consists of the Knight blocking the Black Knight and Challenges it whenever it retargets, while the Druid/Sorcerer uses Death Strikes.
The most efficient duo-strategy to kill it faster would be a Knight blocking him while a Paladin uses Divine Missiles.
Not a good creature to do a fast hunt since it takes a really long time to respawn.
It is possible for a Paladin to solo this creature at level 50. It is reccomended that you take either Royal Spears or Enchanted Spears and a good shield, though you should kill the Bonelords first to avoid mana drain. If you can, also kill the Scorpions too. This will dramatically increase your chances of succeeding. Also, try to remember to go with enough capacity to take his loot and / or your reward from the quest if you are taking it.