Sculpted by: Arlen Pelletier
Used material(s):Cast in antique gold-plated solid metal
One of: Unlimited
Issued in Ghost Door box
First appearance: Keys to the Kingdom #3
Use: Controls squirrels
The Undertree Key was used against the Locke children during February.
Seems to allows the user to control squirrels.
Source: Locke & Key Wikia