In the Pokémon Rumble series, Wonder Keys are keys that bring Toy Pokémon to life. The player has three Wonder Keys in a course. If the player's Pokémon faints, he or she will lose a Wonder Key. However, if the player switches a Pokémon that has not fainted, the player does not lose a Wonder Key. Also, if playing multiplayer mode, the players share three Wonder Keys between them. When either player loses a Pokémon, they lose a Wonder Key, and will fail if they lose all three keys. Wonder Keys can be upgraded by completing the Battle Royales from C Rank to S Rank. When upgraded, stronger Pokémon can be utilized and their full power can be unleashed. Once the Wonder Key is fully upgraded all Pokémon regardless of power can be used in the stages and Battle Royales.
Types of Wonder Keys
Regular key: This is the key which the player starts with. It switches Toy Pokémon slower than the Cool Key, Temple Key and the Hero's Key.
Cool Key: A key which the player receives as a prize after completing both stages of the Battle Royale of the Challenger's Ground. It switches out Toy Pokémon slightly faster.
Bent Key: The Cool Key when it is bent by Cobalion. It switches three times slower.
Temple Key: A substitute for the Bent key. It is received after beating the Temple Of Keys Battle Royale. It is a gold version of the Cool Key.
Hero's Key: A key which is elegantly decorated in a "Royal" fashion. It is received after completing Battle Royale EX-6.
Team Battle Bosses are Powered up by an "Evil" looking key, the true Cobalion is powered up by a special Key, and all area bosses are powered up by a key slightly different than the player's key.
Dark Rust: A living Wonder Key consumed by rust, and the main antagonist of Pokémon Rumble Blast. It is not used to wind anything up, however it does take full control over Rusty Pokémon.