Note: The Shinigami and Thunder Behemoth entries are now up. That should please Anonymous and acanofjars, among others.
Named after a Mesoamerican demon—the story is pretty cool; check it out here—Pathfinder’s xtabay invokes the seductive fragrance of the original myth, but in the form of a flowering vine rather than an evil spirit lingering around a spiny cactus. By itself the xtabay is not that much of a threat, but a copse or a garden of them are another story, especially if the PCs are low-level or unlucky with their save dice. (A TPK by plant because everyone was asleep is going to be a hard story to live down at the gaming shop.)
Even though xtabays are basically your generic sleep-inducing plant (D&D had the amber lotus flower as far back as AC 9 Creature Catalogue), the creepy “faces” on the xtabay’s petals and the plant’s out-of-game mythic origins suggest some possibilities for going beyond that stat block…
When a miserly spinster dies, xtabays bearing her face rise around her gravestone, springing back no matter how often they are uprooted or cut away. At least two young men have since gone missing, and townsfolk say the deceased woman called them to her to warm herbed in the afterlife. The gin-soaked local naturalist has a more cynical view, noting that the old woman was even more skilled with plants than he is. He believes she likely intended to guard her fortune as carefully in death as she did in life.
Morlocks begin raiding a surface town. Just as adventurers arrive to flush out the degenerate horrors, the attacks stop. If they investigate, the adventurers find a cavern full of xtabays, vines grown thick on morlock flesh. The adventurers need to clear out the vines to ensure the flowers don’t spread to the surface, but doing so opens the way for other subterranean horrors to reach the surface world—starting with some ankhegs and a harras of cave sagaris.
Extraordinarily large xtabays (assume they have the Advanced template) sometimes manifest their own dryads. These neutral evil fey are just as ravenous as the flowers they spring from, and their charmed companions rarely last more than a day or two. Unusual for fey, these dryads tend towards demon worship, revering the demoness Xtabay as their mother. In fact, some sages speculate that the dryads and flowers alike are not the creations of the Xtabay, but rather vegetable extensions of her own foul consciousness.
—Pathfinder Bestiary 2 289
The name “xtabay” also appeared attached to a hag in Dragon #317. It’s not one of my favorite issues, but if you’re a player looking for a new character concept it might well be worth checking out—I don't know if I’ve ever seen more prestige classes or variant builds (plus four new PC races!) in one issue.