The lore in the Banjo-Kazooie universe isn't really consistent and there is a conversation about word of god with Gregg Mayles and what is explicitly shown in Rare's games but this discussion will treat all content as canon for the sake of a cohesion.
Mumbo Jumbo is a shaman that first appears on top of Mumbo's Mountain. Prior to going to Witch Doctor School after the events of Banjo-Kazooie, Mumbo only knew how to do simple spells and transformation magic. Still a witch doctor in training at the Handsome Shaman Institute, Mumbo foolishly was the one to introduce and teach magic to Gruntilda. Once Gruntilda outgrew Mumbo's usefulness she had transformed his face into a mask of terror.
Mumbo Jumbo's original form is up to debate. When asked if he was a Jinjo, Mumbo said he felt like he was insulted. There are context clues to what Mumbo's true form may have been. If his origin is Mumbo's Mountain; his village is populated by Grublins; and Grublins' prototype appearance was similar to Mumbo, it's most likely Mumbo was a Grublin. Mumbo's face will not transform back until Gruntilda is truly defeated. As we know, Gruntilda is immortal becoming both a skeleton and a ghost in previous games.
Mumbo's outfit in games prior to Banjo-Kazooie was chosen by Mumbo after the Handsome Shaman Institute encouraged its students to make their own ritual outfits. Mumbo's sole reason of not wearing that outfit was because it doesn't feel right to do so when not an active shaman. The grass skirt also allows Mumbo to safely store his staff in his butt to prevent other magic users from taking it.
Mumbo's source of magic is innate but amplified by an additional source. In Banjo-Kazooie: Grunty's Revenge, he has the ability to speak to spirits but used magical totems that Klungo and Grunty use. In Banjo-Kazooie he uses a collection of skull-shaped tokens in exchange for his transformations, however, Mumbo states that he wasn't using them for magic purposes but simply because he was going through a gothic phase and wanted to make a throne out of silver skulls. He gave up this project because it was too creepy, so he threw them out. This may have been hinted at in the instruction booklet as to why Mumbo can remove and recast spells without repayment. In Banjo-Tooie, Mumbo needed glowbos to perform permanent magical effects such as bringing people back to life and oxygenating large bodies of water. Mumbo and Humba Wumba most likely do not use more advanced magic in Banjo-Kazooie: Nuts & Bolts due to a magic recession, though Mumbo does use some of his magic to assist Banjo and Kazooie with their vehicle creation, though he is still an unlicensed witch doctor who is not yet certified by the Shamanic Union. Mumbo claims that nobody wants to pay for magic anymore, and that banks will not invest into things like transformations.
Prior to the events of Banjo-Tooie, all of Mumbo's Huts in each game world was a vacation home. In Banjo-Tooie, Mumbo's Huts are actually created by Mumbo to assist Banjo and Kazooie on their adventure to get revenge on Gruntilda. Mumbo's Garage in Banjo-Kazooie: Nuts & Bolts is a creation of Mumbo's after he settled into Showdown Town, it was just a coincidence that Lord of Games needed him for his role in Banjo-Kazooie: Nuts & Bolts. After the events of Banjo-Kazooie: Nuts & Bolts, Mumbo's Garage gained enough capital to sponsor events on Rivals Island.
The game worlds outside of Spiral Mountain and Showdown Town in Banjo-Kazooie: Nuts & Bolts are characters playing roles for the game itself rather than being established canon. One big example of the worlds in N&B being non-canon would be Humba Wumba marrying Mumbo in Nutty Acres. Humba Wumba does not like Mumbo because of his reputation. One of the biggest motives of Humba Wumba helping Banjo and Kazooie is to expose Mumbo as an amateur. Humba Wumba's transformations far exceed Mumbo's from previous games. Mumbo only learned new spells after the events of Banjo-Kazooie despite years of practicing magic. Humba by the time she is seen in Banjo-Tooie is a published magic author. The rivalry continued on for years, as Humba even opened up a shop parallel to Mumbo Jumbo's just to talk down his business.
A synopsis would be Mumbo is a foolish shaman who stumbled upwards, never got re-registered after going back to shaman school, and was an asset in creating the Gruntilda we all know and also assisting in her multiple defeats.
Trivia
- Mumbo predominantly uses his right-hand to perform magic spells with his wand.
- Mumbo thinks Humba Wumba has a crush on him.
- Mumbo took a vacation in Click Clock Woods because he felt the effects of changing seasons in real-time.
- Eekumbokum and Oomenacka come from Mumbo's native language.
