Unicorn

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 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 an infamous jewel thief of the 1920s. (DW: The Unicorn and the Wasp)