Basilisk

The Basilisk is a giant serpent, also known as the King of Serpents. It is a creature bred by dark wizards. Herpo the Foul was the first to breed a Basilisk. He accomplished this by hatching a chicken egg beneath a toad. Basilisk breeding was banned in Medieval times, by writ of the Ban on Experimental Breeding.

Because the Basilisk is a serpent, a Parselmouth may place a Basilisk under his or her control.

Traits
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 immediately kill anything who looks into them. If the victim looks indirectly at the Basilisk's eyes, i.e. as a reflection or through an object, they will only be petrified. Ghosts may become petrified by the Basilisk's gaze as well, if they stare directly at it as was Nearly-Headless Nick. This is because ghosts are already dead, so they cannot die again. But a Phoenix (and perhaps other non-human associated creatures) is immune to this deadly gaze. Spiders are terrified of the Basilisk, as they describe it as their enemies, and would not even speak of it.

The Basilisk's sharp fangs are full of deadly venom, powerful enough to kill a human in a matter of minutes. The venom is potent even long after death. It is also one of the few substances destructive enough to destroy a Horcrux. Basilisk skin is armoured like that of a dragon's, which deflects spells cast upon it. The Basilisk sheds its skin at intervals, like all other snakes, when it grows. Basilisks can live a natural life of at least nine hundred years. Their mortal weakness is the crowing of a rooster. Basilisks feed off vertebrate animals. The male can be distinguished from the female by a single scarlet plume on its head.

Muggle Myth
In mythology, a Basilisk is depicted four ways: a huge lizard, a giant snake, a three-foot high rooster with a snake's tail and teeth (also known as a cockatrice), and a shape-shifting dragon. Every new version of the Basilisk in a story added to its deadly array of weapons, such as accounts of fire-breathing and the instantaneous killing power of its call.

Muggles of course do not believe the Basilisk to be real. Another creature named the Common basilisk (Basiliscus basiliscus) is a small lizard that has no magical powers or properties, although it can run on water for short distances.

Basilisk's venom
Basilisk venom is an extremely poisonous substance that only has one known cure: phoenix tears. Basilisk 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 fang was removed from the snake's body. The venom is one of the few known substances that can destroy Horcruxes.

Appearances

 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * Harry Potter and the Chamber of Secrets (game)
 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Deathly Hallows
 * Fantastic Beasts and Where to Find Them

Notes and references
Basilic Василиск