Monsters with petrification attacks are not new fodder for this blog, and this Greek classic has been mentioned in those conversations, but I haven't done a full write-up on her before. She is a rather interesting monster for a few reasons, so let's get to it, shall we?
First off, I'm going to mention the pedantic issue of the name and then drop the issue. I know that in mythology Medusa was the individual character's name, not a race. I'm not sure of why D&D handles the name this way - perhaps because of the other D&D Gorgon - but for whatever reason, like the Pegasus, Medusa has become synonymous with the creature type.
Secondly, you know I loves me some Harryhausen, but just to be clear, he completely made up* the whole "half snake, half woman" design for 1981's Clash of the Titans. The original creature was a woman with snake hair and a face that would make a train take a dirt road.
Medusas (Medusae?) have a reputation for being TPK material, which may be why I have not seen them used much. Granted there is one in B2's Caves of Chaos, but other than that I personally haven't run into them much. When you look at the stats, though, they have some weaknesses along with their obviously strengths.
Medusa (from Moldvay)
Move: 90' (30')
Att: 1 snakebite + special
Damage: 1d6 + poison
No. App. 1d3 (1d4)
NOTE: For convenience I'm going to refer to the medusa as "she/her" instead of "it", even though the Medusa isn't really human (I'm not going to even get into the idea of an all-female species!)
With her poor AC and so-so hit dice and low morale, its obvious she isn't a combat powerhouse. We'll get to her petrification ability in a moment, but first I want to talk about the snakes. Despite having a head full of them, she only gets the one 1d6 bite per round. Sure it's save or die. But it's death in one turn, which gives the afflicted character a chance to keep fighting, or get a Neutralize Poison cast on him before keeling over. Beyond that, she has no other attack.
"But wait!" You say. "Her gaze is an attack!"
The description is quite clear. It is the act of looking at the medusa's face that petrifies its victims, not her looking at you. She can (and often does) try to find ways to trick people into looking at her face (she's Chaotic, after all), but Flesh to Stone beams don't shoot out of her peepers. Some petrifying creatures, like the Gorgon and Cockatrice, attack to "stone" their victims. Not so the medusa.
That being said, it's still a dangerous ability. Typically, she will trick a party into looking her while covered with a hood or veil or some such. Then, WHAMMO! A few bad saves and she has a new statue garden. PCs that avoid getting stoned are left either hamstringing themselves by shutting their eyes or trying to mess with a mirror. On top of all this, the medusa is getting a fat +2 to saves against any incoming spells.
It's interesting to note that by strict interpretation, even though multiple medusae can appear in an encounter, each one is only vulnerable to seeing its own face (not the others').
Given its tactics described on B39 and in The Keep, it's fair to assume a medusa has human level intelligence. This begs the question "What does it want?" I expect a lot of good RP fodder and plot hooks could be found here. Obviously if she had or knew something important to the PCs, she might ask a favor in return, as she certainly can't easily move about in normal society to get what she wants or needs.
* “Every statue I’d seen [Medusa] was just a woman with a pretty face and had snakes in her hair. Well, that wasn’t very dramatic, so I gave her a rather demonic look. We gave her a rattlesnake’s tail, so that she could be a menace from the sound effect point-of-view. It was a shock to see her come out from behind the wall crawling on her hands because that was the only way she could propel herself.”
- Ray Harryhausen