Reissued in Ghost Door box since 2021
First appearance: Did not appeared in comics (yet)
Use: A mystery
Door: An even greater mystery
Will the Enigma Key appear in future Locke & Key stories? Good question. Only Joe and Gabe know the answer to that.
Will it appear as a future release from the studios? It will not.
The only way to grab the Enigma Key is during the first month pre-order for the Bode mini-bust. After that, this key is officially sold out, not to be released in any way, shape or form again.
Source: Skelton Crew Studios order page (offline)