Bdellavritras’ sweet voices belie (naturally) their loathsome natures. Masters of possession, teleportation, and plane-shifting, belier devils are very, very hard to confront directly.
The Tellish ambassador has been revealed to be possessed by a belier devil, but under the fiend’s control he fled to his magical yacht. Catching him on the high seas could take months and puts his life at risk, but a journey to the Ethereal Plane might unearth his possessor.
A prince of the Amber Throne is forced to kill his beloved sisters one by one as each inexplicably tries to assassinate him. Divinations reveal a belier devil is possessing them by turns.
A bdellavritra in Belial’s court augments his powers of persuasion and domination with bardic talents as well. Becoming a favored courtier has helped him hide from the azata who placed a price on his four heads.
—Pathfinder Bestiary 2 85