Imshael is a demon that appears in Dragon Age: The Masked Empire. It is also referenced in Tarohne's notes in Codex entry: Forbidden Knowledge. It identifies itself as a "spirit of choice".
Background
“The first of the magus cast themselves deep in the Fade in search of answers and power, always power. They found the forbidden ones- Xebenkeck, Imshael, Gaxkang the Unbound, and The Formless One. Many conversations were had and much of the fabric of the world revealed. And thus the magic of blood was born.” ―Unknown Mage
Involvement
Imshael appears in The Masked Empire to assist a Dalish clan in unlocking the secrets of the Eluvians, and creates a gem to activate the portals. However, it tricks the elves, as well as Celene, Briala and their comrades, and escapes its binding to slaughter most of the clan.
Ser Michel de Chevin vows to pursue Imshael to atone for his part in the destruction of the clan.