A GM had a city guard ask a vial of blood from every visitor in order to verify identity in cases of small crime and the like.
If that city guard, or other members of government had access to that blood vial, what sort of dangers would my character be exposed to? I'm basically looking for spells/other actions which are enabled by having some blood and are harmful/show things about my character.
The only thing I found myself was Blood Biography, but while annoying, from a broader fantasy background I assumed some more malicious stuff was possible. Is it?