The Theatre 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 Theatre Key can be obtained through multiple means that include but are not limited to:
- A possible 'rare' drop from the Corrupted Onyx Knight.
- On a wall display above the iron cell door in the Inside (first-riddle room)
- A possible 'rare' drop from the Industry Giant.
- A possible 'rare' drop from the Mansion Ant.
- A possible 'rare' drop from the Nightmare Lantern.
- A possible 'rare' drop from the Red Wolf.
In appearance, the Theatre Key appears to be a key made out of hardened bronze with noticeable ornamentations on certain parts of the key, such as a red button with a clown-like expression.
The Theatre Key is mainly used to unlock doors sealed with the keylocks that can only be opened by the Theatre Key. The only door that requires the Theatre Key is the key-locked door in The Grand Hall, at one of the central hall's ends from the statue's viewpoint.
After a player had unlocked and entered a theatre key-locked door, they may explore The Theatre, a zone that provides different activities that players can do in the zone.
- If discarded or accidentally sold, the players can interact with the Pig in Topple Town to acquire another Theatre Key.
- The Theatre Key will not drop upon death.