It will use protection prayers for 20 hits then it stops. If you wear dagon'hai robes or elite black armour, then these will be not aggressive towards you. They can also be killed to increase your rank with the White Knights if you've completed the Wanted! quest.
Using Magic in dagon'hai robes is a great way to take these on. Since they use prayer, you can use Veracs. A player can use throwing knives to attack them resulting in their prayer getting dropped more quickly.
A Black Knight with lots of combat experience.
Clue scroll (level-3), Rune mace, Elite black full helm, Elite black platebody, Elite black platelegs
Coins (411-2487), Gold bar, noted Gold ore (1-3), noted Steel bar (3), noted Mithril bar (1), Mithril bar (2), Steel battleaxe, Black 2h Sword, Black kiteshield, Prayer potion (2), Restore prayer mix (1), Lobsters (1-3), Chaos rune (1-3), Death Rune (1-3), Potato with butter, Chili potato, Super restore (1), Super restore mix (1-2), Restore prayer mix (1), uncut gems, Tooth half of key, Loop half of key, Potato with butter