Narwhal
An arctic whale with a long single tusk — a real creature shaped like a myth.
A narwhal in a dream is the dream's image of a real creature shaped like a myth. The narwhal's tusk fed centuries of unicorn stories; the animal is itself, and is also the thing the legend was built from. The dream brings the narwhal when something in your life — a rumoured talent, a fabled relative, an event others have been telling stories about — is, on inspection, a real and ordinary thing that nonetheless carries the shape of the legend. A narwhal seen in the actual water is the dream affirming the honest sight. A narwhal whose tusk has been broken off and sold as myth is the dream noting that the real creature has been mined for its legendary part, and what survives is the story rather than the animal.