Big Chill

Big Chill is a Necrofriggian alien from the planet Kylmyys.

Ben first transforms into Big Chill during the episode Kevin's Big Score, to chase down Kevin after he stole the Rust Bucket.

Appearance
He is a moth-like alien, Big Chill has an eerie blue skin and green eyes. Big Chill's wings and antennae can fold up into a cloak of sorts, giving him the appearance of a phantom.

During his reproductive cycle, Big Chill takes over Ben's personality, causing Ben to unwillingly transform into Big Chill to carry out the task of creating a proper nest for the babies. This nest is comprised of metal that has been molten and swallowed by the parent Necrofriggian.

Abilities
A moth-like alien, Big Chill's wings and antennae can fold up into a cloak of sorts, giving him the appearance of a phantom. He can become intangible, fly, has superhuman strength despite his frail appearance, and can breathe freezing vapor. He can also freeze the objects it phases through at his discretion. Counter-intuitively, Big Chill is easily capable of withstanding extreme heat, at one point drinking molten metal directly from a massive smelting cauldron. He can also make ice beams from his hands, as shown in Birds of a Feather and Single-Handed. It is also shown he can control the flows of his ice beams in Above and Beyond, when he is facing off with Alan Albright.

Ultimate Form
In Ben 10: Ultimate Alien, Big Chill evolves into Ultimate Big Chill. He is now red with fire patterns. He still has the same powers but instead of he breathing ice he now creates "ice flames".

Trivia

 * Big Chill is capable of flying with his wings folded, as seen in Vengeance of Vilgax.
 * Big Chill is one of the three Omnitrix aliens to appear in Ben 10: Alien Swarm, alongside Humungousaur and Nanomech.
 * Big Chill is one of the six ultimate aliens and twelve aliens to appear in Ben 10: Ultimate Alien.