Well, Im actually Tenter hunting on pearl right now, so I'll give you what you need.
NPC is a she, Frog Shaman, who transforms back into Befana after doing the Tentacle and Dark Shaman quests.
Also, I believe it is supposed to be the shield that it drops, not the earring. According to the trend on most of the bosses, you get a weapon/hat/shield from the boss, and an accessory from a quest.
EDIT: Heres the Shadow Mon for anyone curious. As Res said, you dont see them unless you mouse over them, otherwise theyre invisible. If you stand still, you can see some vague movement around you.