Grolnok, the Omnivore (Innistrad: Crimson Vow)

Legendary Creature Ñ Frog - 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.