Kazordoon mines, under the city
There are many rumours about this NPC. You can read more about it in the Kazordoon Library. It is said that it is impossible to reach the Basilisk directly as there is no way into his room, however some players claim to have successfully entered his cave.
Rumours say that this NPC will create a different (of 5) magic effect on itself when you say a single(?) letter (not q, x or z). Its radius from spawn position is 2.