The very first beast Faith must face is a shadow demon. Huge and horned, these creatures can travel wherever there is shadow. They cannot go in water and extra light makes them shrink. Faith got lucky that the mother demon had to travel by magic or she might have had to fight that too.
Harpies in the Chronicles aren't the stuff of Greek legend. Faith describes them as blue-mouthed evil angels. Their voices can be deadly but can also persuade their victims into walking out to them. A magic sword is pretty necessary with battling a harpy, but noise-blocking headphones are helpful too. Worst comes to worst, sunlight sends them packing.
These demons have bat-like wings and strange pointed ears that protrude above their bald, round heads. Pobowars are black from head to toe, like they've been dipped in ink. They are very like harpies in that they also have compulsion magic. It is not attached to their voices though.