The sleepy village of Raven's Lake has a secret: A terrible god lives in the depths of the settlement's namesake. The citizens of Raven's Lake know that something lives in the lake. People who go out on the lake after dark go missing far too often and frequently turn up weeks later with no memory of where they've been. The local church of St. Cuthbert has been abandoned no fewer than seven times in the last two years, each time its lone cleric packing hastily and fleeing town without a word. Adventurers who come to Raven's Lake have a habit of vanishing forever. The truth is that something does indeed live in Raven's Lake but it is far from a deity. It's an exiled aboleth by the name of Zlorthishen.
The isolated tower of the wizard Deros Frist is an example of a typical tsochari incursion into the human world. This short adventure site describes the lair of a tsochar noble that has successfully replaced Frist, a local wizard of some renown. The tsochar Yikk Tasst now pores through the wizard's libraries and spell books, eagerly absorbing all the arcane lore it can. Pgs. 130-134
Sarkt is an illithid sorcerer. It was cast out of its community for its heretical studies (Sarkt was in fact, lucky to escape alive). It didn't take the cunning creature long to pick up a few thralls and find a new place to live, safe from the murderous intentions of its companions. Sarkt dwells in the subterranean ruins of an ancient shrine to Blibdoolpoolp, the crustacean-headed deity of the kuo-toas. This shrine lies on the fringe of a region controlled by kuo-toas, but since Sarkt's arrival, the fishmen avoid the area. A few unfortunate kuo-toas now serve Sarkt as thralls and maintain the illusion that the shrine serves Blibdoolpoolp.
Akeni was born a servant to a powerful drow family deep underground, but her personality was anything but servile. When she was caught in an affair with the house matron's mate, she killed the matron and her own paramour and fled, eventually stumbling into the lair of a powerful beholder mage named Ormathulak. Akeni knew immediately that the creature was just the ally she needed to wipe out her hated family.
A few weeks ago, a neogi flying ship met with misfortune in a furious thunderstorm as it was setting out on a long journey. Heavily damaged, it crashed on an isolated rocky beach. Several neogi and their slaves were killed or injured in the crash, but five of the small monsters survived, along with four umber hulks and a handful of other useful slaves. Under the leadership of the sorcerer Neex Hist, the neogi are working to repair their ship so they can continue their interrupted voyage. In the meantime, they have set up camp in a large sea save close by the site of the shipwreck. While the repairs continue, the neogi and their minions are scouring the area for anything of interest - there's no point in leaving potentially valuable merchandise in the vicinity of the crash site, after all. Suitable for lvls 6-8 in 5e, using 5e stats.
Beneath the jungle-covered ruins of an ancient human temple lies a small outpost of grell that have taken to hunting the nearby area by night. Sangkon Bhet is a fairly typical example of a small grell outpost; the monsters occupy convenient ruins or caverns for a time as they search out new places to move a colony that has over hunted its previous locale.
Sekarvu is a typical beholder. It spent much of its youth exploring underground realms and killing everything it found. One day, it came upon a large cavern filled with violet fungi. At the edge of the cavern, it found a small band of adventurers who had all but succumbed to the toxins of the fungi's tendrils. They offered little resistance to Sekarvu as it approached and began to feed on their still-writhing bodies. With its first bite, the beholder's life changed forever.