If you only have two Magician's Valkyrie on the field, then your opponent can't attack either of them, forming an attack lock. If you have a third spell caster on the field, then they still can't attack any of your monsters. If the third monster isn't a spell caster, however, it can be attacked. It makes me wonder if this card will be limited (I hope it won't be).
Drystan? He's not limited because his attack redirection only protects NK with less than 1800 ATK, while Drystan himself has 1800 ATK, meaning you can't protect a Drystan with another Drystan.
I remember now, that deck uses an actually niche card, inverse universe. Come to think of it that card can actually cripple a sunsaga ang shogunsaga if it resolves that is.