Blood Dagger

This magic dagger has a vile in the core of the blade. By putting a creature's blood in the vile (6 seconds of concentrated effort for someone attuned to the dagger) the blade is made extra-effective against that creature (all damage dice roll max). In addition, if an affect is applied to the blood, it is applied to the creature when stabbed unless the creature succeeds on a DC 14 Con save.