Sacrificial Athame

Whenever you use this dagger to reduce a creature
to 0 hit points, the dagger slays the creature and sacrifices its soul, unless it is a construct or an
undead. Souls sacrificed this way act as a material component for Summon Greater Demon. When sacrificing a soul, the dagger allows you as a
Bonus Action to cast Summon Greater Demon at
5th level. This feature can only be used once
until the next dawn.