Whifferdill
From Tardis Wiki, the free Doctor Who reference
Whifferdill were a shape-changing species from the planet Xenon. (COMIC: Voyager) Their real form was a humanoid, pale yellow in colour with a round, featureless head.
Frobisher, the Whifferdill companion to the Sixth and Seventh Doctors, referred to his species as "the scourge of the Galaxy" and "public parasite number one". (COMIC: The Shape Shifter)
A Whifferdill's shape-changing abilities could be impaired if they were infected with mono-morphia. (COMIC: Genesis!) They were related to Kymbra Chimeras, another shape-shifting species. (COMIC: Changes)
