Boss Key
From the Super Mario Wiki
A Boss Key is an item in Donkey Kong 64. There are 8 boss keys in total, all obtained by defeating a level boss, with the exception of the eighth, which is found at the end of Hideout Helm. The bosses of each level are accessed by the Troff and Scoff rooms, and the final one can only be accessed if the player has obtained both the Nintendo Coin and Rareware Coin. The boss keys are used to help free K. Lumsy, resulting in opening new levels and completing the game. After the key obtained from Dogadon in Angry Aztec has been used on K. Lumsy's cage, both the Frantic Factory and the Gloomy Galleon worlds can be accessed.
