The Ancient Key is an item which allows you to enter The Road from The Supermarket and a door in the Grand Hall leading to the Vault.
Obtaining
To obtain the Ancient key, the player must first catch Running Man who can spawn anywhere in the mansion. After the player has found and caught Running Man, they need to find Toaster Josh who will trade you the Running Man for the Ancient key. Toaster Josh can spawn throughout the Mansion, but he is more likely to spawn in The Back Area.
If the Ancient Key is discarded or sold by the player, you can talk to the Pig to get it back. It will not be lost on death.
Some enemies may also drop the Ancient Key. Enemies that can drop the Ancient Key are: Boomer, Corrupted Gold Knight and Corrupted Onyx Knight.