Requires either Mod The Gungeon, or an internal file replacement -- (MTG is a lot easier, so I reccomend using it)

Place the images for the Blasphemy reskin inside of "Enter the Gungeon\Resources\sprites\WeaponCollection02"
The projectile textures go inside "Enter the Gungeon\Resources\sprites\ProjectileCollection"

If these folders do not exist yet, you can create them.