Yep, this should be in Props/accesories/armour. For his... weapon? I would try to glue some real branches together for making the form. The clothes look so easy to find, and you only will have to paint the sweater with fabric paint and distress the pants. There are a lot of tutorials about how to distress fabric, and you can use a toothbrush and a piece of cardboard to spread the paint for making the frosty parts. Also, you can glue the rope of his pants so it can't fall, and you will have to style carefully the wig (if you're using one). Good luck!
Working on: Anna (Frozen)
Future cosplays: Rapunzel