1. Get 3 vocations: Magick Archer, Warrior and Warfarer. 2. The skills you need are (MA) Sedative Bolt/Soporific Bolt, (WA) Savage Lash/Indomitable Lash and (WF) Rearmament. Note: Rearmament is not necessary as you can swap your weapons in the equipment menu. The sorcerer Asperity augment is also useful but not completely necessary. (Increases chance of inflicting Sleep). 3. Tell your pawns to wait. Charge up Sedative Bolt/Soporific Bolt. Walk in and dodge the Dusa's arrows/gaze if necessary. 4. Shoot the Sedative Bolt/Soporific Bolt at the Dusa's head. If it doesn't fall asleep, simply repeat until it does. 5. Swap to your greatsword and run up to its head, charge up Savage Lash/Indomitable Lash and cut its head. 6. It mutilates at 100% freshness and 100% of the time. If you plan to carry it with you it's recommended to have the sorcerer augment Constancy to decrease the rate at which the head rots. If not make sure to use a ferrystone to head to a inn/town and put it storage. The head stays fresh like any other time sensitive item and persists past NG+.

Great idea! thank you!