Magic Weapon

Casting Magic Weapon on the same weapon again has no effect. No matter how many times you cast it on the same weapon it’s still just magic +1d4 damage.

That said, even a weak enchantment is nothing to be scoffed at. Having a magic weapon may give you an advantage against some of the stranger beasts of Dungeon World, ghosts and the like. The exact effects depend on the monster and circumstances, so make the most of it.