These items are found when Mario defeats Bowser in the boss levels. When Bowser is defeated, he morphs into a Bowser Key and Mario can use it to unlock doors. The key is only for the door it is compatible with. In the DS remake, Yoshi (wearing a cap), Mario, Luigi, and Wario can get the keys defeating bosses and Bowser. The keys are unlocked with 8 stars (12 in the DS remake), and 30 stars. In the DS remake, the player uses Bowser Keys to unlock Mario, Luigi and Wario's rooms. In New Super Mario Bros., when Mario or Luigi defeats a boss, they earn a Bowser Key, which unlocks new worlds. In the final boss instead of getting a key you get a star which when touched will cause mario to get a wing cap and end the game.