Rumbling Ruin is a uncommon Creature — Elemental card from Ravnica Allegiance (RNA), collector number 112. Current market price: $0.15 (foil $0.25), TCGplayer market prices via Scryfall.
When this creature enters, count the number of +1/+1 counters on creatures you control. Creatures your opponents control with power less than or equal to that number can't block this turn.