A basilisk is considered a legendary giant serpent, known as the King of Serpents. It is a creature bred by Dark Wizards. This snake hatches from a chicken egg that had been perched by a toad, first bred by Herpo the Foul. Basilisk breeding has been banned since Medieval times. It is capable for living for at least nine hundred years if put under a deep sleep regularly.
Only a Parselmouth has the ability to place a Basilisk under his or her control. The Basilisk can grow up to fifty feet in length, and is a dark green colour with large yellow eyes. These eyes have the power to instantly kill anyone who looks directly into them, and petrify any who look through indirectly such as a reflection or through an object.
Basilisk skin is armoured allowing it to deflect spells cast upon it. The Basilisk sheds its skin at intervals, like all other snakes, when it grows. Their mortal weakness is the crowing of a rooster. Basilisks feed off vertebrate animals. Male Basilisks can be distinguished from the female by the presence of a single scarlet plume on its head.
Phoenixes are immune to their gaze and their tears serving as the only cure to Basilisk venom. The venom is so powerful that it can kill a person within minutes, making the person drowsy and blurry-visioned before they die. It has a very long lasting effect which still remains potent even up to five years or more after the snake has died.
Wearing glasses will not protect a person from the fatal effect of the basilisk's stare, because glasses still allow one's line of vision to connect directly and clearly with the serpent's eyes, unlike looking in a mirror or through a camera. It has also been theorized that spiders fear basilisks because arachnids can see 360-degrees around them and cannot shut their eyes, leaving them extremely vulnerable to the monster's killing gaze.