Meltron

 guarded the opening between N-Space and the blank dimension. He was created by the psychic mindpower of Brimo.

When the Fourth Doctor and Sharon Davies arrived, Brimo offered them a cup of tea. When Brimo was unable to attack the Doctor with psychic energy bolts, she ordered Meltron to kill the Doctor, while the Doctor willed him to make another cup of tea. The conflicting orders between the battle of the minds split Meltron into two figures, and the two Meltrons were caught in a stalemate. When the Doctor tricked Brimo into thinking of the Eternity Capsule she was imprisoned in, everything else in the dimension vanished, and Brimo ran out of power to escape. (COMIC: Doctor Who and the Time Witch)