Board Thread:Breeding Questions/@comment-24191562-20131210103353/@comment-10090661-20131210111320

You should Breed it with a Dark Dragon. The possible results are Pure Dark, Vampire & Dark Fire Dragons.

Possible results for Pure Flame x Black Knight = Pure Flame, Pure Dark, Flame, Vampire, Dark Fire. The more possible results there are, the more likely you get something other than what you wanted. :)