Bathroom Entity

The Bathroom Entity was the most bizarre of the four entities that the Doctor encountered. It had various strange abilities, including reality altering, perception warping and body/clothing modification.

Biography
The Bathroom Entity had the most strange abilities out of the four, as it changed the Doctor's clothes, gave him bloody spots on his hands, made him see alternate universes and almost trapped him in a mirror prison for eternity. When the Doctor looked into a handheld mirror, it altered his reflection, smiling at him with twisted features. The Doctor left the bathroom almost immediately after realising the danger, and the entity remained there for another 20 years before leaving. (Horror at Towell Farm)

Trivia

 * The face seen in the mirror is a homage to Split-Face from John Carpenter's horror classic The Thing.
 * The entity is from the same planet as the Midnight Entity from 2008's Midnight, although it is unknown if the species are related.