Grist, the Hunger Tide

Legendary Planeswalker — Grist

As long as Grist isn't on the battlefield, it's a 1/1 Insect creature in addition to its other types. [+1]: Create a 1/1 black and green Insect creature token, then mill a card. If an Insect card was milled this way, put a loyalty counter on Grist and repeat this process. [−2]: You may sacrifice a creature. When you do, destroy target creature or planeswalker. [−5]: Each opponent loses life equal to the number of creature cards in your graveyard.