Enchantment
At the beginning of combat on your turn, mill a card. When you do, if there are four or more creature cards in your graveyard, put a +1/+1 counter on target creature you control and it gains deathtouch until end of turn. (To mill a card, put the top card of your library into your graveyard.)
Sigil of Myrkul's triggered ability triggers and goes on the stack without a target. After you mill a card, if there are four or more creature cards in your graveyard, the reflexive triggered ability will trigger. You choose the target for that ability at that time.