Jiggy

Jiggies are collectible items found in all of the Banjo-Kazooie games and can be considered the series' symbol. These golden jigsaw pieces contain a strong magic capable of breaking open the entrances to the games' worlds and are essential in progressing through each game. Jiggies are obtained through completing various missions, helping characters, playing mini-games, fighting bosses, or sometimes (especially near the beginning of the games) found lying on the ground in certain areas. Depending on the game, the number and manner in which the Jiggies open worlds is different.

Banjo-Kazooie
Every level has a matching portrait hidden somewhere in Gruntilda's Lair. Jiggies fill in missing pieces of the level's portrait like a Jigsaw Puzzle, and an increasing number is required for each consecutive world. Jiggies here are actually "spent" to open worlds, unlike subsequent games in which only the total amount of Jiggies collected is considered.

Banjo-Tooie
Once a certain amount of Jiggies are collected, Banjo and Kazooie can enter Jiggywiggy's Temple. The duo must solve a moving picture game for Jiggywiggy to open the next world. An increasing number is needed for each consecutive world.

Banjo-Kazooie: Grunty's Revenge
Jiggywiggy again opens the worlds, just like in Banjo-Tooie, but solving a puzzle is no longer required.

Banjo-Kazooie: Nuts & Bolts
Jiggies are taken, from Jig-O-Vends, to the Jiggy Bank in the Central Plaza of Showdown Town, to open the world act doors, and, similar to the previous games, an increasing number is needed on every door.

Sonic & Sega All-Stars Racing with Banjo-Kazooie
Although not a collectible in this racing game, Banjo and Kazooie's ultimate attack involves Kazooie waving her magic wrench and then sending waves of Jiggies to crush other opponents.

Trivia

 * The maximum number of Jiggies found in each game has decreased with each released installment (with the exception of Banjo-Kazooie: Nuts & Bolts). There are a total of 100 in Banjo-Kazooie, 90 in Banjo-Tooie, only 60 Jiggies in Banjo-Kazooie: Grunty's Revenge, and even fewer are found in Banjo-Pilot. There are, however, a total of 131 Jiggies in Banjo-Kazooie: Nuts & Bolts.
 * In Banjo-Kazooie, when Banjo obtains a Jiggy, he will jump around dancing while holding it above his head, stopping just long enough for Kazooie to eat it. The only exceptions to this are when Banjo and Kazooie are flying or swimming underwater, or while using an animal transformation.
 * In Banjo-Tooie, the Jiggy spins around Banjo before flying into the air and disappearing without disrupting gameplay. This new method could have been easier to program and could be used for any character or situation in which the Jiggy is obtained without looking strange if used on unusual terrain (ex. while sliding down a slope). This also was done because standing with it was time-consuming.
 * In Banjo-Kazooie: Nuts & Bolts, when you gain a Jiggy and bring it to the Jiggy Bank, it floats into the bank, playing the jingle from the first two games.
 * In Gobi's Valley, we find out that Jiggies have been around for at least 10,000 years, since Grabba says he had his Jiggy for over 10,000 years. What they were used for in the ancient past is unknown.
 * Jiggies are used as an attack move for a pinata called Fizzly Bear on Viva Pinata, another game developed by Rare.
 * No matter where it comes from, Jiggies always appear to be clean. (i.e. Boggy barfing it up, Canary Mary's wing, destroyed in a crushing shed, pooped out by eerie.)

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