Unicorn
From Tardis Wiki, the free Doctor Who reference
A unicorn was a mythical beast similar in appearance to a horse, but with a single long horn in the middle of its head.
The Second Doctor encountered a unicorn in the Land of Fiction. (DW: The Mind Robber)
Unicorns were one of the many life forms inhabiting Tír na n-Óg. (NA: Cat's Cradle: Witch Mark)
In 2002, unicorns appeared in San Francisco due to a dimensional scar. (EDA: Unnatural History)
"The Unicorn" was the alias of Ada Mullins. (DW: The Unicorn and the Wasp)
The Bestiary of Legendary and Magical Creatures created a unicorn out of toilet paper. (ST: Phoenix)
Iris Wildthyme had a unicorn statuette in her TARDIS. (ST: Old Flames)
The Doctor once claimed he was a unicorn (NSA: Borrowed Time]] 
