Sculpted by: Arlen Pelletier
Release: 2021
Edition: Limited
Used material(s): Cast in silver and gold-plated solid metal
One of: Unlimited

Issued in Ghost Door box

First appearance: Key to the Moon (one-shot, Guide to the Known Keys)
Allows entry to the afterlife
 The Moon

More information:
(possible spoilers)

The Moon Key allows the user to open the moon, as though the moon itself was a door. You can pass into the door taking you to a “backstage” of the world, passing into the afterlife gently.

This key is forged and used in the side story Locke and Key: Guide to the Known Keys. In the story a generation of the Locke family has a sick child, Ian ,who cannot be healed by the mending cabinet. The child is taken to the moon by balloon as though the world is a stage and passes gently to the next world.

Source: Locke & Key Wikia