Enchanted Weapons
The Intelligence scaling of these weapons is applied to both their Physical and Elemental damage (except Lightning) when using any Infusion or Ammunition.
Example: A magic infused Blueblood Sword will increase both its Physical and Magic damage with Intelligence, while the lightning infusion will make it only increase its Lightning damage with the Faith stat.
Holy Weapons
The Faith scaling of these weapons is applied to both their Physical and Elemental damage (except Magic) when using any Infusion or Ammunition.
Example: A lightning infused Sunlight Straight Sword will increase both its Physical and Lightning damage with Faith, while the magic infusion will make it only increase its Magic damage with the Intelligence stat.
Luck Weapons
The Luck scaling of these weapons is applied to each and all damage types the weapon might have when using any Infusion or Ammunition.
Example: A fire infused Hallowed Sword will increase both its Physical and Fire damage with Luck, on top of the scaling gained from the rest of stats (Strength and Dexterity for Physical, and Intelligence and Faith for Fire).
Notes
- Do not confuse with the Enchanted, Holy and Lucky Infusions, as they are unrelated to the uniqueness of the listed weapons.
Information here is accurate for version 2.15.