Slime Key
The Slime Key is required to gain entry into the Key Cavern in Link's Awakening. To obtain the key Link must travel to Kanalet Castle to retrieve Five Golden Leaves for King Richard. In return King Richard will grant Link access to his dangerous back garden where an owl statue is located. Using the shovel to dig under the statue, the Slime Key will appear. The Key has a close resemblance to the Final Boss of the Key Cavern. Ironically, the key seems to be made of stone or metal, rather than slime, even though it is named the slime key.