Time demon

A time demon, a name which the Sixth Doctor found ridiculous, was a creature of the Time Vortex which the Doctor thought of as a "never-were," an "after-thought," and an "idea that got above its station." Like other temporal predators, it feasted on the chaos created by manipulating time.

The time demon either possessed Stapleton Petherbridge or adopted his identity, and created a pocket of cauterized time in which it either recreated Pease Pottage or relocated it from 1987. The demon claimed the Doctor's TARDIS had passed through it many times, though whether this was metaphorical or literal is unclear. Using Mel Bush's incredible ability for "total recall" to manipulate time as well as two versions of the TARDIS, it planned to enter the real universe.

The Doctor trapped the demon in its own reality. (AUDIO: The Wrong Doctors)