Grist, the Hunger Tide is a mythic Legendary Planeswalker — Grist card from Secret Lair Drop (SLD), collector number 1417. Current market price: $17.80 (foil $18.16), TCGplayer market prices via Scryfall.
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.