White Knight and Black Knight were one of the first Mirrored pairs, all the way from Alpha. In Scourge, they added Silver Knight, and it wasn't until Planar Chaos that they created Blood Knight. Although you could easily contend that Silver Knight and Blood Knight are another Mirrored Pair, and the entire set is simply two Mirrored Pairs, I've always felt that this has actually become an incomplete mirrored set — with another black knight and red knight missing. I felt Everend offered me an opportunity to finish the cycle so that each of the colors had a pair of enemy-hating knights.