Equip this card to an opponent's Warrior-Type monster, allowing you to reduce its ATK and destroy an opposing Set card. If you manage to destroy that monster by battle because of that ATK loss, you can re-equip this card to a "Noble Knight" monster you control.
Equip this card to a monster Special Summoned by the effect of "Noble Knight Medraut". Since that monster is in Defense Position, the ATK loss will be meaningless.
If this card is equipped to a "Noble Knight" Normal Monster or "Ignoble Knight of Black Laundsallyn", use this card's effect, then Tribute that monster to activate either effect of "Black Laundsallyn" (and re-equip this card to another "Noble Knight" monster after that effect resolves). With this, the ATK loss will be rendered meaningless.
(If this card is equipped to a "Noble Knight Medraut" or "Noble Knight Gwalchavad", use that monster's effect to destroy this card and have it become a Normal Monster again, so as to use the above combo, assuming that monster isn't equipped with another "Noble Arms" card.)