Grolnok, the Omnivore is a rare Legendary Creature — Frog card from Innistrad: Crimson Vow Promos (PVOW), collector number 238s. Current market price: — (foil $6.24), TCGplayer market prices via Scryfall.
Whenever a Frog you control attacks, mill three cards. Whenever a permanent card is put into your graveyard from your library, exile it with a croak counter on it. You may play lands and cast spells from among cards you own in exile with croak counters on them.