Grolnok, the Omnivore is a rare Legendary Creature — Frog card from Innistrad: Double Feature (DBL), collector number 505. Current market price: $2.72 (foil $10.43), 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.