This one is highly RNG based. Make sure you have activated both the Cataclysm expansion itself AND the characters. Choose to play as The Black Knight. Move back and forth in the Middle Region, trying to land as often as possible on the Castle, and make sure you always have at least 1 gold handy. Each time you land here you draw a Denizens card. One of the Denizens you can draw is also called The Black Knight. Pay 1 gold to have them take a life from another character, and the achevement will unlock.
If you get the Poltergeist follower, it'll make this go faster.