An Adze, as seen in Final Fantasy XI.
The Adze were vampires in Ewe/African folklore. Unlike most batty vampires, these take the form of a firefly when in the wild, and will revert to human form when captured. In this form, they may possess other humans. While they didn’t directly control those they possessed, the possessed were generally suspected to be witches and ostracized for it, usually by their family or those they were jealous of. They are arguably worse in firefly form, in which they pass through walls and suck the blood of the sleeping. They quickly fall ill and die, and there is no defense against it.
An agloolik, as seen in Final Fantasy XI.