Funhouse

The Funhouse was a creature with the appearance of an old house. It had the ability to create illusions. It fed off power and intended to take power from the Doctor's TARDIS. It misled the Sixth Doctor and Frobisher and created an illusion of Peri. It became one with the TARDIS. It was eventually trapped in the Time Vortex, where it began the long wait for new prey. (DWM: Funhouse)

behind the scenes
The Funhouse bears a striking resemblence to House from TV: The Doctor's Wife. They both fed off of energy, both wanted to eat the energy from the TARDIS, and both took control of the TARDIS and became one with it.