Faceless stalker (ugothol)

Whereas dopplegangers are merely humanoids on a wicked, hedonistic streak and without much regard for life, ugothols are actively trying to sabotage whatever society they infiltrate. Their goals are far more obscure and far less understandable to mere humanoids.

The summer and winter courts of the Wickerlands fae have been at war for generations. Their power rises and falls with the seasons - as the first snow falls, the winter queen Titania wakes from her sleep, and when Firebirds return from the south, Titania goes back into a torpor just as her counterpart Maeve wakes from hers. It is only the recruitment of fey-born mortal champions into the war that brings a disturbing truth to light - Maeve and Titania are one and the same.

The city of Rothalingia is notorious for it's exceptionally well organized crime. Everyone seems to agree there must be some sort of secret cabal running things behind the scenes - but no-one even suspects that the black heart of the city is an orphanage. Indeed, the city's hidden masters take perverse glee in taking forms of children and toddlers as they unleash extreme violence upon the city's unsuspecting populace.

Several times across the years, members of the Witchfinder guild have foiled a hidden enemy's schemes. Growing annoyed at their interference, the faceless stalker tries a new gambit - over several months, he drains the blood of hapless victims and leaves their bodies in a public place (in stark contrast to his usual MO). As rumors of a bloodsucker start spreading across the city, the ugothol allows himself to be seen in vampire form several times - each time closer and closer to the guild's headquarters. If he isn't caught quickly, the guild's dhampir members are sure to be arrested - and most probably burned at the stake. 

Ettin

 Ettins, eh? A great example of how a simple stat block with one neat ability can make for a really, really memorable encounter. The ettin's heads acting on different turns in the initiative is a really neat touch, though, and will make your players rethink their tactical approach as the creature gets to adapt and react to their actions at twice the rate of any other.

Blognaag and Thrognaag are an especially loquacious ettin with a highly specific MO. Standing vigil at the twin doors that lead into the famed Jotunhard dungeons, Blognaag and Thrognaag will greet any potential visitors by explaining to them how one only speaks the truth while the other one always lies, and how one door leads to great treasures while the other leads to certain death. In truth, the whole mystical schtick is a ruse itself - the ettin is a manipulative liar but perfectly capable of telling the truth if need arises, and both doors lead to a deep pit ending in spikes, and the cunning ettin merely enjoys playing others' intelligence on themselves, coming in to finish off the "nerds" and take their treasure after the deadly fall.

Deep in the vaults of the Sorceruos Constructs penitentiary, the most feared artifact is hidden. The murderer's coin is a simple enough object - a small piece of gold, with an alien deity on it's face. However, when no-one is looking at it, the coin has the tendency to teleport itself into random people's pockets, and whoever but touches it with bare skin, dies instantly. So far, the only way to contain it has been to have four ettins, working in tireless shifts to just stand and stare at the coin. However, as the ettins grow restless from the lack of action, a more permanent solution must be found.

Krook and Pnook are two ettin heads in a heavy predicament. When Krook sat on Pnook's favourite chair (an old throne from a raid years past), Pnook decided the offense was grave enough to warrant murdering Krook. Ever since then, he has been sabotaging Krook's every effort and attacking him at every point - whereas poor Krook is seeking help from the same villagers he had raided for years, feeling Pnook manages to find him whereever he tries to run or hide.

Ether spider

 Ether spiders - previously called phase spiders - have an interesting niche. Despite being creatures of the ether plane, filled with evil and degenerate beings, and feeding on humanoids, ether spiders are neutral, not evil, and intelligent enough to reason with. That means that for your average party, an ether spider attacking is a thing of pragmatism - if they are worth more as food then they are as guides, gambling companions, or even outright heroes, they won't be eaten.

Shadowstep spire is an ancient hold constructed over two different planes. The old lord of the keep was a borderline insane wizard, who made the keep in such a way that passage through it requires constant passage between the shadow and material planes. Unfortunately, his riches quickly drew the murderous attention of a large family of ether spiders - who now jealously covet the keep's bounty, while simultaneously looking for someone brave enough to explore its deepest corners.

Spangle Spadangle is an ancient ether spider sage. Millenia ago, he was known as the multiverse's leading expert on planar travels. However, the Order decided that his knowledge was too dangerous - and yet the arachnid had grown to powerful to easily kill. Eventually, they decided to tear off all of his eight long limbs and scatter them across the planes, and lock him between seven layers of chains.
If the spider's limbs are reattached, though, the chains won't hold - and he would be willing to share his knowledge with his potential saviours.

Clerics of Daur, the deity whose duty is to watch over the passage of souls to the heavens, have grave news - A massive, world-spanning web has appeared in the Spirit Lands, trapping any and all souls who must pass through on their journey. Anyone braving the webs finds them crawling with phase spiders possessing an eerie, golden glow, who ignore the living until attacked and sing songs about the "Final feast"