The Ether Medallion is one of two Medallions required to complete A Link to the Past, and the three overall. The Medallion in conjunction with the Master Sword creates a stream of cold air to cover the screen, freezing most tougher enemies and killing weaker enemies in the process. The Medallion is required to enter Misery Mire.
High atop Death Mountain, west of the Tower of Hera, a lone monolith stands waiting for the Hero to claim its secret gift. The translation which Link reads using the Book of Mudora sates that if the Master Sword is held up, the bearer will receive the power of Ether. Using the Ether Spell, Link can control the prevailing winds and can even change the weather in certain areas of the Dark World. The monolith will crumble once the Ether Medallion is claimed. "
"Whoosh! The power of wind is now at Link's disposal."
To obtain the Ether Medallion, Link must first obtain the Book of Mudora. Next, he must venture to the west of the Tower of Hera on Death Mountain, where he will find a large stone slab that contains Hylian reading. Once Link deciphers the inscription, the Ether Medallion will be acquired.