Tennis Shoes
These magic items subtly alter the path of projectiles, thus aiming them at the person wearing the Tennis Shoes. It won’t unnaturally curve the trajectory of a projectile, but ‘in the general direction of’ is usually good enough to ensure a hit. If somebody is actually aiming the projectile at someone, a hit is almost assured. The top velocity of the projectile must be no more than about one hundred miles an hour, which means that it works on baseballs — but not, say, arrows. Also, the projectiles generally aim for the center of mass; this is not a spell for headshots.
Whether or not these are beneficial or inimical magic items depends on what they’re being used for. Any athlete competing in a sport involving balls will find Tennis Shoes invaluable; someone trying to dodge a grenade might have a different opinion. Certainly France’s Deuxième Bureau has been using Tennis Shoes as assassination tools since the Thirty Years’ War — what? No, that’s not a typo. Let’s just say that temporal-based thaumaturgy is more trouble than it’s worth, and leave it at that.