Gamer jargon. A term used to describe something or someone who has ascended to a higher dimension through sheer willpower, going a step above Sicko Mode.
When you or something is suddenly on point as fuck. You / whatever you are referring to is on the next plane of existence / ballerdom. The urban equivalent of going super saiyan.
Nigga mode means every tyoe of adrenaline related feelings and actions.
Example: anger, excitement, being a crazy bitch and attacking your friends, running around, jumping, uncontrollable sadness, and such, summing it up: every extreme emotion.