Medusa: the snake-haired quarry of Herakles, the horror with the petrifying gaze. In the fifth-edition Monster Manual, this unnatural being is explained as one who made an infernal bargain for immortality and beauty, then paid the price when the latter wore off but the former didn’t. There’s no satisfactory natural explanation for the medusa, so in this case, evolutionary imperatives don’t necessarily apply; the medusa seems more like a being driven by compulsion, as undead creatures are.
Medusas have high Dexterity and Constitution, typical of a skirmisher. They have enough Intelligence to plan and lay traps, enough Wisdom to choose targets carefully and avoid battles it won’t win, and more than enough Charisma to parley when it’s advantageous. These abilities are paired with proficiency in Deception and Insight, along with Stealth. Thus, a medusa stays hidden from threats and uses its wiles to lure trespassers to their doom. (The flavor text describes a medusa’s lair as “shadowy ruins . . . riddled with obstructions and hiding places,” meaning it contains lots of places of concealment to take advantage of.)
The medusa has two distinctive features, Petrifying Gaze and Snake Hair. The latter is a simple melee attack that does some poison as well as piercing damage. Petrifying Gaze is more complicated and demands closer examination.
First, the range of Petrifying Gaze is 30 feet. That means that the medusa has to draw its opponents close enough to use this feature. Although the medusa has a ranged weapon attack (longbow), it’s not in the monster’s interest to start a sniper battle, because then its opponents will remain at too great a distance. Instead, the medusa should wait until its opponents are within range.
Second, the petrifying process isn’t necessarily instant. The DC of the Constitution saving throw to resist petrifaction is 14. An average player character without class proficiency in this saving throw has a 40 percent chance of making this saving throw; a player character of intermediate level (therefore assuming a +3 proficiency modifier, rather than +2) with Constitution as his or her prime requisite ability, proficient in this saving throw, has a 60 percent chance. Failing the saving throw by a difference of 5 or more results in immediate petrifaction; the chances of this are 40 percent and 20 percent.
If petrifaction isn’t immediate, the target of the Petrifying Gaze has to fail a second saving throw to be petrified; a success on this second throw frees the target. So we have four cases to look at here: success; failure, then success; failure, then failure; and criticial initial failure. The latter two result in petrifaction, and the former two result in escape. For the average PC, the chance of two successive failures is 15 percent; for the high-Constitution, proficient PC, 10 percent. Putting these probabilities together, the total chance that a medusa will petrify an average PC (in either one round or two) is 55 percent; a high-Constitution, proficient PC, 30 percent.
These aren’t inspiring probabilities, which brings us to our third item: A creature halfway through the petrifaction process is restrained. Attacks against a restrained creature have advantage, and the creature’s own attacks have disadvantage. This tells us that a medusa wants to promptly follow up its use of this feature with melee attacks, to exploit this momentary edge. And it is momentary—logically, it can’t last more than one round, because after that, the target either turns to stone or shakes the effect off entirely.
Fourth, “a creature can avert its eyes to avoid the saving throw at the start of its turn”—unless it’s surprised. Therefore, making that first appearance with surprise is essential.
Fifth, a creature has to be able to see the medusa for its Petrifying Gaze to have an effect. This means that, despite its darkvision, the medusa is ill-served by hiding in darkness. It needs at least dim light to be sure that trespassers will be susceptible to its gaze. On the other hand, bright light leaves the medusa vulnerable to catching its own gaze in a reflective surface and turning itself to stone. The medusa can’t risk that. Dim light is the happy medium.
Finally, although the feature can be very easily misread as affecting only one creature at a time, it can in fact affect every creature within its range. Note the wording: “When a creature that can see the medusa’s eyes starts its turn within 30 feet of the medusa, the medusa can force it to make a DC 14 Constitution saving throw . . . .” Not “one creature that can see the medusa’s eyes.” “A creature”—any and every creature.
On the other hand, seeing the back of the medusa’s head doesn’t hurt anyone. So we can think of this feature as having an approximately semicircular area of effect with a 30-foot radius. (Or we could think of it as a cone; going by “Targets in Area of Effect” on page 249 of the Dungeon Master’s Guide, the number of targets is the same either way.) This tells us that if the medusa can’t catch at least three opponents in her gaze when she first unveils it, it’s not worth it to her to try.
Time to put it all together. When a medusa detects trespassers in its lair, it hides—someplace where it will be able to pop out and catch at least three opponents (ideally, all its opponents, but three is the minimum) by surprise in its field of view. Because of the possibility that an opponent might have a higher initiative roll and thus not have to make a saving throw until the surprise round is over, and because it would rather not have to try to get away from multiple melee opponents, the medusa will make its appearance within 30 feet of its would-be victims, but outside their melee attack reach. That way, it won’t have to fight both unrestrained opponents and opponents restrained by a single, noncritical failed saving throw at the same time. Only those not affected at all by Petrifying Gaze will be able to attack the medusa after its first turn. Starting in its second turn, the medusa will focus its attacks first and foremost on its restrained opponents.
Unlike some features (e.g., Frightful Presence), Petrifying Gaze doesn’t confer immunity on a successful saving throw. This means that the medusa benefits from prolonging combat, because it will get one opportunity after another to petrify its opponents. It will fight a single opponent toe-to-toe, but anytime it’s attacked by two or more, it will Dodge (action) and move to a place of concealment. If its opponents don’t chase it down, it will use its next turn’s action to Hide, then move stealthily to a new position where it can pop out and catch its opponents in its Petrifying Gaze once more. An opponent who averts his or her gaze to avoid being turned to stone is just begging for a stab in the back: as an unseen attacker, the medusa has advantage on attack rolls against opponents who are intentionally looking the other way. Once an opponent is turned to stone, of course, the medusa moves on to other, still-moving targets.
A medusa is torn between the desire for release from its curse and the fear of death that drove it to seek immortality in the first place. When it’s seriously injured (reduced to 50 hp or fewer), it will start looking for a way out of its situation, Dodging (action) incoming attacks as it retreats in the hope that its opponents may carelessly expose themselves to its gaze.
Next: intellect devourers.