Shadow Medallion

The Shadow Medallion is an item in The Legend of Zelda: Ocarina of Time.

In-game
The Shadow Medallion is a circular, dark purple medal with an upside-down triangle surrounded by circles on each side emblazoned in the middle. Link receives it from Impa, the Shadow Sage, after defeating Bongo Bongo in the Shadow Temple. Though its only purpose is to mark Link's quest progression, there are theories that it could've originally been equipped and used to help Link in-game someway, although this was obviously scrapped.