The Cave of Skulls is a common Plane — Earth card from Doctor Who (WHO), collector number 573. Current market price: $0.26, TCGplayer market prices via Scryfall.
Each creature card in your graveyard has scavenge. The scavenge cost is equal to its mana cost. (Exile a creature card from your graveyard and pay its mana cost: Put a number of +1/+1 counters equal to that card's power on target creature. Scavenge only as a sorcery.) Whenever chaos ensues, create two 1/1 white Warrior creature tokens.