The Return of the Vostok
The Vostoks were a species of cold-causing creatures
The Vostok looked like giant jellyfish, with black bodies and large, thick tentacles. They could survive on land or underwater, but they were sluggish on land. Vostok reproduced by fission.
They would drain the heat out of everything around themselves, covering places in ice and snow. They could cause sudden snow-storms and blizzards within days. On the other hand, when killed they would release all the energy they had stored up, causing a sudden heat wave. (The Return of the Vostok)
The Vostok lived on Earth for a long time, being known to the Vikings as “the Gods of the Ice Age”. They went into hiding under the polar icecaps.
In March 2009, a group of Vostok came to Cardiff, freezing over Cardiff Bay. They were attempting to gain control of the Rift, which they would use to cause an ice age throughout history, killing all the humans. Torchwood was able to stop them by attracting them to a water tower charged with Chronon energy, which they believed was from the Rift. While the Vostok were all in the same place, Ianto Jones drove a oil trunk to the water tower, which was then lit on fire, killing all the Vostok. (The Return of the Vostok)