After all this talk of elementals, fiends and fey, it’s nice to get back to garden-variety monsters. Today I examine the harpy, a foul-tempered predator with an alluring voice. As with all monstrosities, I’m going to assume that it uses its abilities to survive in accordance with evolutionary imperatives.
The harpy has a balanced physical ability profile, with slightly but not significantly higher Dexterity than Strength or Constitution, and it has no ranged attack. Instead, it uses the long-range ability Luring Song to bring prey into melee attack range.
Its Intelligence of 7 indicates that the harpy is instinct-driven, and its Wisdom of 10 indicates that it’s indiscriminate in target selection but knows when to flee. This is consistent with one part of the Monster Manual flavor text: “If a fight turns against a harpy, it lacks the cunning to adapt and will flee and go hungry.” It’s less consistent with this part: “A harpy takes its time dismembering a helpless foe and can spend days torturing a victim.” If this were instinctual to the harpy, it would be disadvantageous to its chances of survival. Granted, Intelligence 7 is the upper bound of instinctual behavior, so I suppose it’s possible that a harpy might toy with its prey or lure it into natural hazards before attacking it. But these feel too sophisticated to me.
This part, however, makes a lot of sense: “Harpies have no interest in a fair fight, and they never attack unless they have a clear advantage.” All predators have an innate sense of what creatures are vulnerable enough for them to prey on and what creatures aren’t. And since the harpy’s physical ability contour doesn’t suggest any one characteristic fighting style, it makes sense that it would have to find some other edge, something neither dependent on their own strengths nor compensation for their weaknesses.
So here’s the compromise I’m going to settle on: Harpies congregate around natural hazards that other creatures frequently fall into, because these provide them the best hunting grounds. Luring other creatures into these hazards isn’t something they do intentionally—it’s just something that happens a lot, the natural consequence of their own abilities combined with the terrain. Harpies that roost near hazards simply survive better, having more opportunities to feed.
Now let’s figure out what kind of creature is suitable prey for a harpy, 1 vs. 1. The harpy is a challenge rating 1 monster. Against a single player character, its encounter multiplier would be 1.5 (per Dungeon Master’s Guide, page 82), for a total of 300 adjusted experience points. That would make a single harpy a deadly encounter against a level 1 or 2 PC, hard for level 3. (If you want to use the Unearthed Arcana “Encounter Building” article instead, four harpies are a hard challenge for four level 4 PCs, deadly for level 3 or lower.) In other words, one humanoid is definitely suitable prey for one harpy. And since harpies aren’t smart enough to make judgments like, “Oh, dear, that person is walking with confidence and carrying a very fine weapon; she might be too skilled a fighter for me to handle,” a harpy might fearlessly attack a humanoid even in a group of four or five. (Probably not more than five.) After all, against armor class 10, a harpy has a 70 percent chance to hit with each of its attacks and can be expected to do 7 hp of damage in one turn—more than enough to kill a commoner. And this is without the victim’s being debilitated in any way, mind you. For the sake of encounter building, however, you’ll want to calibrate the number of harpies to the number of PCs in your group and how difficult you want the encounter to be.
Finally, let’s look at the Luring Song feature, because the way it’s written makes it seem more complicated than it is, and it buries its implications. First, it has a range of 300 feet: a creature hears the song long before it ever sees the harpy. An immediate Wisdom saving throw is called for, on which elves have advantage (owing to Fey Ancestry). If the saving throw succeeds, the creature is immune to the effect. If it fails, the victim is charmed (he or she can’t attack the harpy or harm it with magic or any other ability) and incapacitated (he or she can’t take actions or reactions) and must move toward the harpy by the most direct route (per the MM errata). And the victim gets to repeat the saving throw at the end of each of his or her own turns, with any success conferring immunity to the effect.
The DC for this saving throw is only 11—not very high. A character with a +1 Wisdom saving throw modifier (i.e., this is an average ability score for the character, and not one he or she has class proficiency in) has a 55 percent chance of success each time he or she rolls; with a +4 Wisdom saving throw modifier (i.e., this is a prime requisite ability and one he or she does have class proficiency in), a 70 percent chance of success. With the advantage conferred by Fey Ancestry, these probabilities rise to 79.75 percent and 91 percent. In other words, unless Wisdom is a PC’s dump stat, it’s unlikely that he or she will fail this save twice, and three failures would be a dismal run of bad luck. So anytime the harpy might use Luring Song, it has to cash in on its effect immediately. Even one more round is too long to wait.
Here’s how I see all this fitting together: The harpy waits hidden, 20 feet above a natural hazard, until its prospective prey wanders within 25 feet of that hazard. It then uses Luring Song to try to entice the victim into the hazard. At the edge of the hazard, just before stepping in, the victim gets another saving throw (if the hazard will cause actual damage and not just a debilitating condition), which he or she will probably succeed on.
At this point, as the dungeon master, you need to decide how smart your harpy is. If you want it to be more animalistic, just have it fly down and Multiattack immediately, then fly back up out of reach, regardless of whether or not the victim makes his or her saving throw. If you want the harpy to have a smidgen of cunning, then it can also attack immediately if the victim fails his or her save and steps into the hazard. If the would-have-been victim succeeds on his or her save, on the other hand, then the harpy can attempt to shove its opponent into the hazard (Player’s Handbook, page 195) in lieu of its club attack. For the remainder of its Multiattack action, it will attack normally with its claws, then use the rest of its movement to fly back up out of reach.
One Multiattack is normally enough to finish off a humanoid commoner. On the harpy’s second turn, it flies down and Multiattacks one more time, against the same target, with its club and claws. If this isn’t enough to bring its opponent down, the harpy has just barely enough wits to recognize that this isn’t going to be easy prey after all, and it flies away. It never prolongs the fight beyond two rounds. On its third turn, it Dashes, fleeing at double its normal flying movement speed.