Mumbo Jumbo is a shaman who originally taught Gruntilda how to use magic. She disavowed Mumbo Jumbo and cursed him by turning his face into a skull mask. He has three red feathers on top of his head. He helps Banjo and Kazooie by providing them with transformation magic in Banjo-Kazooie and he is a playable character in Banjo-Tooie, where he can use his "mighty shaman zap-stick" to levitate objects, oxygenate bodies of water, enlarge objects, heal, give life force, and zap enemies. He runs Mumbo's Motors, a garage in Banjo-Kazooie: Nuts & Bolts. He can play a saxophone, the xylophone, and can also pick up a violin. Mumbo Jumbo can be one of your partners in Kameo: Elements of Power by downloading a free skin for one of the characters on Xbox Live.
Source: Wikipedia, "Banjo-Kazooie (series)", available under the CC-BY-SA License.