Crystal Magic Weapon is a Sorcery in Dark Souls 2. To cast a Sorcery, you must use a Staff or Special Weapons that can cast Sorcery.
Crystal Magic Weapon
"Imbues weapon in other hand with crystal magic. More powerful than standard magic reinforcement.
The utilization of crystals to enhance soul power is an ancient form of magical reinforcement."
- Chest in Dragon Shrine. Above two Drake Keepers; one with a mace and one with a sword and shield. To get it, run over the small bridge on the right and continue through that path. Eventually you will end up above the ledge with the chest. Just drop down and the chest should be on the right.
Rare drop from Ducal Spiders
- Buffs weapon with magic damage. Duration scales with Intelligence: 63 sec. at 28 Int and up to 99 sec. at 42 Int. Superior to Magic Weapon and Great Magic Weapon. Equivalent to Sunlight Blade and Dark Weapon in effectiveness.
- DS2's buff formula differs from other Souls games, instead relying primarily on the targeted weapon's base damage to determine how much AR the spell buff will add. Matching the spell buff with a damage type present on a weapon will add a flat bonus to the total AR, depending on whatever the weapon is infused with and/or naturally inflicts said damage type. A small scaling bonus is also added, unless the targeted weapon doesn't scale at all with any stats.