Big Key

Use
Big Keys are used to open large doors that lead to a boss room. They are only used in Toy Dungeons and Trial Dungeons. Big Keys can only be used in the dungeon they are found in and the current big key count can be found to the left of the celestial fragment count at the top of the screen.

Obtaining
Big Keys may be obtained in various ways:
 * Opening chests in Toy Dungeons or Trial Dungeons
 * Defeating all enemies in a room
 * Solving a puzzle in a room

There are usually only 1-2 Big Keys in a given dungeon and are most often found at one of the last few rooms on a floor, meaning the entire floor often must be explored before obtaining a Big Key.