Also had one drop from an Undead Footman the other day. After killing him 4 times the mask has only dropped once. Seems rare. Have yet to see the Horn drop.
Had one drop off an Undead Footman today. Not sure how common a drop it is, as that's the only one I've seen. Dropped. Dust of Decay, Bonechips and the no drop quest sword for a wandering spirit. Hope that helps