Czisch

Czisch was an alien baby brought to Cardiff in 2009 via the Cardiff Space-Time Rift.

Appearance and Abilities
Czisch took the form of an unnaturally adorable human baby. It was capable of telepathy and mind control, allowing it to find a host to take care of it. Despite being a baby, Czisch was as intelligent as an adult human. (PROSE: The Wrong Hands)

Biography
Czisch was brought through the Rift by its mother, who left it in Cardiff with a Torrosett 51 binary heat-cannon. It took control of Pam Feerce, forcing her to take care of it. Pam cut off all ties with the rest of the world and devoted herself utterly to taking care of Czisch.

Eventually, Czisch encountered Gwen Cooper and chose her as a host, releasing Pam. Ianto Jones and Jack Harkness were able to release Gwen from Czisch's control, so it took back Pam. Before Pam's mind was completely subsumed, she was able to activate the self-destruct button on the heat-cannon, killing both of them. (PROSE: The Wrong Hands)

Czisch's father later infected Jack Harkness and Gwen Cooper with the Kagawa Virus in revenge. (PROSE: Virus)