Big Chill is an Necrofriggian from the planet Kylmyys. He bears a striking resemblance to the cryptid Mothman. His wings and antannae can "fold" up giving Big Chill a hood and a long robe, making him look more like a phantom. In the episode Save The Last Dance, it is revealed that Necrofriggians reproduce asexually, laying eggs once every eighty years. They build a nest out of digested metal, from which their offsprings hatch, ranging from a few to many. The newborn Necrofriggians live in space, feeding on solar plasma. When Ben goes through this reproductive cycle, Big Chill takes over his personality, causing Ben to unwillingly transform into Big Chill to carry out his task.
Necrofriggian is derived from "necro", meaning death, and "frigid", meaning very cold
Big Chill is an intangible, ghost-like creature with a breathy, ethereal voice, who can pass though all solid matter, turn himself invisible, and drop the temperature of anything he chooses to just this side of absolute zero. He can breathe freezing vapor as an attack and can freeze an enemy when he passes through them with his intangibility. Big Chill gets its ghost-like abilities from Ghostfreak, freezing abilities from Articguana/Absolute Zero, and flying and buglike appearance from Stinkfly.
Big Chill's invisibility doesn't conceal his body heat or voice. Though his breath easily tames fire, if he blows too fast he has to "catch his breath" and is momentarily weakened.
Big Chill is actually asexual and a parent as shown in Save The Last Dance in which big chill takes over ben with every transformation he makes and eats all metal in site, it turns out he was actually building a nest for eggs he had laid which.