Nilith

The Nillith is a pretty interesting creature that manages to add new flavour to an old and established concept in TTRPGs: the stalking nightmare.

Several bits set nilliths apart. First, while your initial instinct might be to throw them in the melee, their spell list isn't trivial as it suits their proposed hit-and-run tactics quite well—especially the nasty at-will invisibility.

Second, while they have strong ties to the Astral/Dreaming plane, they are still beings of the mortal realms—this means they must somehow figure in local ecologies. Thirdly, there's the implication that Nilliths are but mere mouthpieces connected to beings beyond most mortals' capacity to fathom...

- Nemanja

Hook 1 (Nemanja) - The Signal of The One

After years of fighting off beings from the Hidden City Of Leng, a wizard has found a way to intercept the connection between a nillith and its mystical master. At first, all went well; the wizard used the accursed being to essentially be in two places at once, using the nillith's body for menial, physical tasks, while delving yet ever deeper into studies of what lies beyond the Veil. Recently, his sanity seems to have slipped. While no blood has been spilled, the nillith has been seen frothing at the mouth and staring at odd-shaped clouds in the dead of night, whereas the wizard has started drawing odd runes on the city walls, claiming to herald the arrival of "The One Who Sees Through Us All". As the madness that took him looms ever closer to an escalation, the wizard's old compatriots are called in to investigate.

Hook 2 (Reece) - The Nilith Number

Nary a knight knows not the night. Nary they nap now or none. Know none of knights that knock or nest upon that nightmare road—none that nab naps near the Knobwood. There knows the knight that the nightmare rests. There knows the knight that no knight might nick the knave, as no knave naps in the knob—only nightmares therein take flight. 

- Bardic song of the Knobwood, said to be haunted by a beast that feeds upon noble knights.

Hook 3 (TJ) - Weary of the Whisperwood

A ring of houses surrounds the town in the middle of The Whisperwood. These houses—though they seem to be abandoned—were never inhabited, and no one shall ever live there. This ring of houses serves as decoys for the foul spirits of the Whisperwood who seek to corrupt the dreams of those who rest close to its borders. In a similar insulatory fashion, the people who call the Whisperwood home do all their business strictly by daylight, leaving plenty of buffer to get home before the sun goes down. When a hunting accident delays the main fighting force of the town, the remaining locals must make a hard decision: brave the woods, or leave them to their demise.