The Ancient Key is a 'monster drop' that was introduced during the Ratboy's Nightmare Update. It is one of the many collectibles that are needed by the players in order to complete the entries of the Itempedia of the Nightmare. The Ancient Key can be obtained through multiple means that include but are not limited to:
- A possible 'rare' drop from the Boomer.
- A possible 'rare' drop from the Corrupted Gold Knight.
- A possible 'rare' drop from the Flying Clown.
In appearance, the Ancient Key appears to be an age-old key emitting a diabolic aura. It appears to be made out of hardened bronze and gold, with several glowing yellow gems on certain parts of the key.
The Ancient Key is mainly used to unlock doors sealed with the keylocks that can only be opened by the Ancient Key. These keylocks are made out of the same materials of the Ancient Key, being made out of gold.