D&D has a long tradition of cribbing its monsters from other sources; Greek myth, classic horror films, and weird rubber toys alike were seen as fair game from which to poach a fantastical menagerie. Today’s monster is the Basilisk, and it comes to us from medieval legend. The Basilisk is an eight-legged reptile with the power to turn people to stone with its gaze. I quite like the illustration of the basilisk in the Monstrous Manual: I appreciate the subtle coloring, the return of Tim Burton-esque stripes on its tail, and the fact that it seems to be munching on something.
Unfortunately, the Monstrous Manual gives very little actual habitat or ecology notes for this monster, which is a bit of a let down. It does note that Black Dragons will sometimes mate with a basilisk to make a Dracolisk, but that is kind of disturbing when you think about it.