Thrusk

Thrusks were a parasitic entity that took the form of a small, goblin-like creature that existed within the dimension of the Space-Time Visualiser.

Biology
The Thrusks were small, goblin-like creatures. They were capable of infecting a person's body and taking their physical form for their own.

History
The Thrusks were originally from the main universe, but completely disappeared centuries ago, and ended up in the Vortex. Over time, they became little more than parasites.

Many years ago, the Thrusk encountered Tamira as she was flying around the Time Vortex in her Type 2 TARDIS. They infected her and took over her body, putting her in stasis so she was unable to regenerate, thus expelling the Thrusk from her body. Over the years, the Thrusk took over Tamira's TARDIS and began searching for another TARDIS, in order to crash the two ships together. The Thrusk's leader sought to obliterate the universe, and restart it, using the Thrusks as building blocks for the new universe. They hid within the Space-Time Visualiser in Tamira's TARDIS.

Eventually, the Thrusk encountered another Time Lord; the Doctor. After Melanie Bush caught a glimpse of the leader of the Thrusk in the Space-Time Visualiser, she entered the dimension inside the machine, and encountered a group of Thrusk. She demanded the Thrusk take her to their leader, so they took her to the room containing Lady Tamira.

Later on, the leader of the Thrusk was made aware of Mel's plan, and attempted to stop her. Mel revealed to the Thrusk that their leader planned to kill them all in order to create a new universe from their own building blocks. Their leader did not deny this, and as Mel returned to her universe, the Thrusk advanced on their leader. (AUDIO: Mel-evolent)