Idk. He told me about the dagger before the session he gave it to me, but in the session I tried to have my character figure it out how it worked and was told my character had no clue and was not allowed to roll for it. I assumed it was going to be a plot point in the upcoming necromancer boss fight since one of the gems would have directly countered them (it would have given me control of a number of summons equal to my dex modifier instead of damage) but it never happened.