Item description:

[Demon Gaze II] Who Wants These?
Prometh: "I was told to give you this trophy once you collect all mushrooms."

[Demon Gaze II] The Mortician's Hobby
Prometh: "Please collect skulls. I've prepared a special trophy for it."

Load up the save and head to B1 at the Inn.

Enter the weapon shop and the morticians shop, select talk, and choose the options to give mushrooms and skulls. Mash through, you have to give around 20.