Key (鍵 Kagi) is an item from the Ghosts 'n Goblins series that is dropped by the boss in the end of a stage. Arthur must take the key to open the gate in the end of the area and proceed to the next stage.
Maximo vs. Army of Zin has two types of keys, and they can't be carried over from one stage to another. Iron Keys are used to open locked Treasure Chests, and Maximo can carry up to nine of them in a stage. Gold Keys are used to open gates, and only one can be carried at a time.