This post concerns an important event item and it may or may not contain spoilers [in this case the spoiler would be concerning game-play and not much on story]
Proceed at your own risk.
Dragon Key #4 - The Iron Key
aka: The Quartz Key and/or The Ghost Key
Description: This key is made of black iron, and is symmetric in its design. There is a glowing white quartz engraving of a equine skull embedded in its handle
Quest: This key is the most mysterious of the four dragon keys. I cant reveal much except that there are five mysterious urban legends of Ponyville tied to it. I'd like to call these legends 'Hollows'
What are these hollows? I really just cant tell you. you'll just have to find out on your own.