Unfortunately, unlike the Iron Golem in that one event a little while back, I have no units who can survive a hit from the Mithril Golem. While I've been able to kill it on Magical Ancient Weapons, I'm not quite sure what to do about Showdown at Fairy Village, what with trying to defend against lesser enemies while staying clear of the Golem...
Also, I have never seen goblin archers that strong before...