Faun, incubus, and satyr?

According to the Malleus Maleficarum, the faun, incubus, pan, and satyr are different names for the same demon. Medieval Christianity demonized the image of the rustic god Pan, which inspired the popular depiction of the devil with goat features. In fantasy gaming, the incubus and satyr are depicted distinctly (the faun is rarely depicted separately from the satyr, and the pan is nonexistent).

I think a way to represent this in fantasy gaming would be if the incubus monster was created from the faun or satyr by some means. Perhaps a faun or satyr who turns evil becomes an incubus, or vice versa? There are any number of ways to represent this transformation.

Adaro: ghost, merman, and sprite of the Pacific islands

The adaro is a malevolent ghost in the folklore of the Melanesian. When a person dies, their better half or aunga passes on whereas their worse half or adaro remains behind. The adaro becomes a malevolent ghost that assumes the form of a shark-like monster. They travel across rainbows and waterspouts, and kill men by throwing fish (often described as flying and venomous).

According to Encyclopedia of Beasts and Monsters in Myth, Legend and Folklore by Theresa Bane, they lived on the sun but visited earth by riding rainbows and waterspouts during sun showers. They could be friendly, visiting people in dreams to teach song and dance. They were often malicious, knocking people unconscious and only waking them if placated with an offering of a flying fox. Their chief was Ngorieru, who haunted the shore of San Cristobal.

Like a lot of folkloric monsters, their traits varied wildly by region. Students of comparative mythology may note superficial similarities to the hún and pò of Chinese folk religion.

In Pathfinder, they became malevolent merfolk with shark features. 3.x statistics emulating the folklore were posted at The Worlds of Mankind.

I find the original Melanesian monster way more interesting than a generic shark-themed merman, mostly because it doesn't pretend to have a pseudo-naturalistic ecology by virtue of being a ghost and its habits of crossing rainbows, riding ocean tornadoes, and throwing venomous flying fish sounds pretty cool. Finding a flying fox to cure an unconscious victim sounds like a pretty quick plot hook.

"Adaro/Anguiliian" by Azel/Atolm

What do you call a mermaid with an octopus half?

Years ago I wrote a post about how the neologism "cecaelia" commonly used for octopus-mermaids on the internet is actually meaningless gibberish. I still believe that, but in this post I wanted to play with folk etymology.

The girl's name Celia is a short form of both Caelia ("heavenly") and Cecilia ("blind, dim-sighted"). The otherwise gibberish name "cecaelia" sounds like it might be a play on these names.

Caelius ("heavenly") and Caecilius ("blind; invisible") were both Roman family names. Perhaps the name of the species is actually something like cilophyte (see my old post for an etymology analysis), but some families of cilophytes have surnames like Caelius or Caecilius. After some confusion while talking with fishermen, the surnames end up being mangled and mistakenly refer to the entire species.

Or perhaps the name derives from a phrase like "Ecce Caelia!" meaning "Look Caelia!" (where Caelia is the person being addressed) or "Here is Caelia."

Or it might be derived from caelo ("I carve") + -ia (abstract suffix), meaning something like "carvery."