The magical negro in fiction
The magical negro is typically but not always "in some way outwardly or inwardly disabled, either by discrimination, disability or social constraint," often a janitor or prisoner. He has no past; he simply appears one day to help the white protagonist. He sometimes fits the black stereotype, "prone to criminality and laziness." To counterbalance this, he has some sort of magical power, "rather vaguely defined but not the sort of thing one typically encounters." He is patient and wise, often dispensing various words of wisdom, and is "closer to the earth."
The magical negro serves as a plot device to help the protagonist get out of trouble, typically through helping the white character recognize his own faults and overcome them. Although he has magical powers, his "magic is ostensibly directed toward helping and enlightening a white male character." It is this feature of the magical negro that some people find most troubling. Although from a certain perspective the character may seem to be showing African-Americans in a positive light, he is still ultimately subordinate to European-Americans. He is also regarded as an exception, allowing white America to "like individual black people but not black culture."
To save the white protagonist, however, he would do anything, including sacrificing himself, as Sidney Poitier portrays in The Defiant Ones, the prototypical magical Negro movie.
The Native equivalent of the "magic negro" is the wise elder or shaman or faithful Indian companion. This includes Tonto, the Quileute werewolves in Twilight, and countless comic-book Indians. It also includes characters played in movies and on TV by Chief Dan George, Ned Romero, Floyd Westerman, Russell Means, Graham Greene, Gordon Tootoosis, August Schellenberg, et al.
About the only difference is this: While "magical negroes" appear occasionally in the media, many fictional African Americans are fully developed protagonists in their own right. For instance, the characters played by Will Smith or Denzel Washington. But most fictional Indians exist to rub their mystical wisdom and might onto the nearby white protagonists. Few can stand on their own as characters.
Magical Indian mascots
This point about fictional Indians applies to Indian mascots also. They're supposed to transfer their bravery and ferocity (i.e., their savagery) to mascot-worshiping athletes. In fact, we might compare Chief Illiniwek's dance to a Satanic, black magic, or voodoo ritual.
Odd that so many God-fearing Christians believe in the dark power of their pseudo-Indian talismans. Have they read what the Bible says about bowing down to and worshiping idols? These people love their mascots as if they were prophets or deities.
Below: "Great Spirit, I implore you! Succor my friends and smite my enemies!"