It was a DLC given to those who supported Valheim early in the beta development. Can't get it anymore and spawning it in with the console won't let you wear it either since it requires the DLC.

https://steamcommunity.com/app/892970/discussions/search/?q=dlc&gidforum=3220528325737848531&include_deleted=1

ahh thanks for that... i got exited for a min lol.