So far, I’ve been lax in examining fey creatures. This is partly because they generally aren’t evil, so they don’t often show up as opponents. It’s interesting that Dungeons and Dragons has always chosen to portray fey creatures this way, because in folklore, fairykind can be very nasty. In D&D, however, they tend to be giggly and harmless.
Pixies are simultaneously gregarious and shy, curious and aloof. They don’t fight, period. If a combat situation emerges—and this will be, 100 percent of the time, because your players are choosing to be jerks—they flee. The simplest way is simply to vanish using Superior Invisibility. But if that’s not enough to make the player characters move along, they also have confusion, dispel magic, entangle, phantasmal force, polymorph and sleep in their repertoire. These are all once-per-day powers, but pixies are never alone. (With Strength 2 and Constitution 8, why would they be? Tiny, fragile creatures seek safety in numbers.) Invariably, there will be enough of them around to unleash all those powers, round after round, plus druidcraft and dancing lights for extra disorientation. They’ll use sleep against non-elven spellcasters; dispel magic against all spells the PCs attempt to cast; confusion, phantasmal force and polymorph against fighters; and entangle against everyone else. Pixies should systematically thwart any attempt to hurt them; as a dungeon master, don’t go out of your way to be fair to players who are picking on pixies.
Sprites are the fighters of fairyland, but even they don’t fight to kill. Their “longsword” does an epic 1 hp of damage when it hits, but they only use this weapon when someone grabs them. Normally, they shoot opponents with their bows, which have a chance of delivering a dose of knockout poison. Like pixies, sprites congregate in overwhelming numbers, so even though each of them deals only 1 hp per hit, a swarm of angry sprites can turn a PC into a humanoid pincushion—an unconscious humanoid pincushion. Again, forget about being fair: go right ahead and make your players make a dozen saving throws against that poison. They asked for it.
Sprites’ ideal combat range is 40 feet: near enough for normal chances to hit with their bows, far enough that most PCs can’t close the distance. If a hostile PC approaches closer than 40 feet, they use Invisibility to disappear, resituate themselves 40 feet from the PC in another direction, then shoot again the following round.
If a PC does manage to hit a sprite, it will probably die on the spot, so choosing whether to flee isn’t a function of how many points of damage one takes but rather how many of them have already been killed. If, somehow, the PCs manage to kill 60 percent of a swarm of sprites, the rest fly away.
Dryads are less good-natured and much less social, but they’re also unlikely to initiate combat, unless the PCs are engaging in wanton destruction in their woods. One possible exception, however, is if a dryad has taken a shine to a PC and charmed him or her, and the other PCs try to interfere.
They’re not weak, but their mental abilities are superior to their physical abilities, so they’ll rely on these and avoid combat if they can, especially melee combat. If a scuffle seems imminent, they’ll ready barkskin and cast it as a reaction when a PC initiates hostilities; if it comes as a surprise, this will be their first full action. They’ll use their clubs if angered (first casting shillelagh as a bonus action) or cornered, but it’s nearly impossible to corner a dryad, especially in its native forest. Dryads never venture far from a living tree, and if PCs try to close in on them, they use Tree Stride—an innate feature, not an action!—to slip away (ideally, they’ll use trees that are also within their attackers’ reach, so as not to provoke opportunity attacks). From a safe distance of 60 feet, they then cast entangle (action) at the unwelcome visitors’ feet and make their escape. Even when angry, they’ll withdraw from combat when seriously injured (reduced to 8 hp or fewer).
“Dryads work with other sylvan creatures to defend their forests,” the Monster Manual flavor text informs us, but given their ability profile, it seems probable that they leave the actual fighting to others, for the most part, relying on enchantment (Fey Charm) to dissuade lone trespassers and deception (druidcraft) to befuddle small groups, and calling in the unicorn cavalry to deal with more numerous enemies. (“Unicorn cavalry” is a metaphor here, though it does conjure up an awesome mental picture, doesn’t it?)