Sculpted by: Jamie Macfarlane and Israel Skelton
Release: 2015
Edition: Limited, Boston Comic Con
Used material(s): Cast in bright gold-plated pewter
One of: 500

Signed: First 400 signed by Joe Hill

First appearance: Keys to the Kingdom #3
Control a person
 Music Box

More information:
(possible spoilers)

The music Key and associated Music Box was used against the Locke children during February and during Tyler Locke’s final confrontation with Dodge.

When this key is inserted into the music box, a small replica of the user appears and repeats the user’s command. Any listeners are compelled to follow the music box’s orders.

Guide to the known keys entry:
“…He was dying fast from his injuries and knew it. He said he would go to glory and take his secrets with him. Ulysses said that if our Lord meant to open the Gates of Heaven to a B—- like him, he would prefer to throw in with the Devil. Clint hisses and seemed ready to strike again, but I restrained him. I knew if Hammersmith died, I would likely never see Delacorte again, and so I turned the Key in the Music Box, and the tune began to play. A miniature version of myself turned around and around and sang: …tell us who paid you for the girl… do it now before you leave this world… Hammersmith’s eyes widened, and he began to speak…”

Source: Locke & Key Wikia