"Mischief" (aka "Pink Guy" or "Smile") as referred to by fans is a recurring character in the Interface series and seems to be a key figure in the overlying plot. They have been seen in many episodes and is often accompanied by "Blue Guy".
"Mischief" is believed to originally have been an American Human within the US Navy, although their form was altered by their involvement in the 1943 Philadelphia Experiment. The Experiment has been subject to much speculation and conspiracy. Within the Interface universe, the ship was teleported from Philadelphia to New York. The process also caused rather negative effects, like the crew fusing to the hull. Mischief's previous being was destroyed as a result of the incident and they instead became the creature they appear as now.
Although "Mischief" appears mainly as a pink, sepertine creature they are known to take many other forms such as a bus or a "beautiful sunflower". It is believed that this shapeshifting power may have been gained through Cerebral Electricity, a mysterious energy which appears throughout the series. It is unclear the full extent of power gained by Mischief through the use of Cerebral Energy as well as how many possible forms it might take.