Mask of the Devil of the Reed Field

You can get the Mask of the Devil of the Reed Field at a house in Sunset Valley. It’s a keepsake rather than a helmet.

This keepsake causes a whole bunch of trick scarecrows to spawn on the Mountain of Frozen Souls, which you can fight endlessly. You can put it in storage and the scarecrows will continue to spawn, or you can discard it to make them stop and pick it up back at Sunset Valley.

From the How to get the Sunset Reed Armor in Crimson Desert: Overview and Stats guide.