Basilisk

A Basilisk is a giant serpent. Those who look its directly in the eyes die instantly, but those who see them indirectly only get Petrified. It is most feared by spiders, even Acromantulas.

Description
The Basilisk is huge, reaching up to fifty feet in length and may live for up to nine hundred years. It has venemous fangs, but its main weapon is the ability to instantly kill any creature (apart from the Phoenix, which appears to be immune to its gaze). The crowing of the rooster will instantly kill the Basilisk.

The Basilisk was first bred by Herpo the Foul, and is accomplished by hatching a chicken egg underneath a toad. The most recent sighting of a Basilisk was in 1993, when a Basilisk was discovered inside the Chamber of Secrets at Hogwarts. Harry Potter killed the Basilisk inside the Chamber of Secrets, saving the school from almost-certain closure.