Basilisk

The Basilisk is a serpentine creature from the medieval bestiaries, and is one of the most feared of all monsters. Its gaze is lethal, and the creature itself is so poisonous that its venom actually travels up the weapons of would-be hunters, killing the hunter and the mount as well. Grass withers, streams become tainted (not becoming safe to drink for at least a hundred years), and birds fall dead to the ground. Its hiss is deadly as well. It is known as king of the serpents. It also has the ability to breathe fire. The Basilisk is born when a cockerel hatches a serpent’s egg. Only a weasel, which is immune to the Basilisk's arsenal, can kill the creature. Also, wearing a suit of mirrors or carrying a mirror-polished shield will cause the creature to die of its own gaze. The corpse should then be burnt to cinders.