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Since they have the Blessing of the Lady ability as well as glowing weapons and are called "Royal" (like Royal Pegasus Knights) it is very heavily implied that they are Grail Knights. For this reason they should get Perfect Vigor and Magical Attacks like the other Grail Knights. In multiplayer they are barely used, and in singleplayer they are mostly abused as doomstacks because of Bretonnia's insane economy and the doomstacking meta, rather than being an OP unit on their own. So there shouldn't be a balancing reason to not give them these abilities (I also don't think that giving them these abilities will push them into OPness).