C^ Hyperspeed is a hyperspeed glitch that allows Mario to build up unbounded speed by sliding down a slippery slope while trying to enter first person mode.
The trick happens when the player enters first person mode by pressing C^. Usually Mario's speed decreases and he comes to a stop, but if he is on a slippery slope (type 0x13) he will accelerate. If he is facing uphill, he will get negative speed, and if he is facing downhill, he will get positive speed. If he is facing exactly 90° to the slope, he will still gain negative speed. The C^ action can be cancelled with a kick, a punch, becoming airborne, or hitting a wall. If it is not cancelled, Mario will slow down and enter first person mode once he exits the slope.