The beard is my favorite part, namely how ridiculously long it is:
The Knitpicks Comfy I used on the hat is great for stitch definition, but may not be stretchy enough. I'm sure a quick wash and light tumble dry would tighten it back up. The trick to the horns is definitely to stretch the base of the horn out as wide as it will go as you're sewing it on, in order to get stability at the base and keep the horns from drooping.
I did a video last night explaining everything I could about the beard, including materials and construction methods. Hope you enjoy it!