Key

There are dozens of different keys for castles and fortresses all across Mushroom World.

Super Mario Bros. 2 is the first Mario game with keys and locked Doors. Phantos will always be guarding keys, so unless you drop the key or unlock a door, a Phanto will be chasing you. Keys are always in view; never under a Vegetable.

In Super Mario World, the Keyholes would turn into a gigantic portal when a key came into contact with it.

In Super Mario World 2: Yoshi's Island and its sequel the keys unlocked doors, but when a castle boss was defeated a large key would appear and act the same as ones in Super Mario World.

There are many key designs in Paper Mario and Paper Mario: The Thousand-Year Door but each only opens doors in the area they are found. There are Castle Keys for every castle and fortress, and various others keys in different locations. A living key called Yakkey locked the Gusty Gulch Windmill in Paper Mario. In Paper Mario: The Thousand Year Door, the Grotto Key is a key that opens a door in the Pirate's Grotto.

In Luigi's Mansion, Luigi had to collect many keys before he could advance to other rooms. They were usually found in Treasure Chests, although some could be found right out in the open.

Bowser Key
Bowser Keys are keys owned by Bowser found in the Mario Party series. Bowser Keys are usually found in Bowser Mini-Games in order to escape from Bowser. In earlier Mario Party games, Bowser Keys are simply keys shaped like Bowser's head. In later game, they are engraved with Bowser's likeness.

Castle Key
Castle Keys are used to open locked doors in castles. In Paper Mario, they were used in Tubba Blubba's Castle, Bowser's flying castle, and Peach's Castle. Tubba Blubba's keys look like three leaf clovers, while Bowser's look like a gold three leaf clover with a blue ball in the middle. There are about three of Tubba's keys and five of Bowser's keys. Peach's Castle Keys are pink versions of Bowser's.

In Paper Mario: The Thousand-Year Door, the Castle Keys that open the doors in Hooktail Castle are shaped like flowers. In Super Mario RPG: Legend of the Seven Stars, there are two types of Castle Keys: Castle Key #1 and Castle Key #2. They are listed as Special Items.