Obsidian Fireheart is a mythic Creature — Elemental card from Zendikar (ZEN), collector number 140. Current market price: $0.82 (foil $7.66), TCGplayer market prices via Scryfall.
{1}{R}{R}: Put a blaze counter on target land without a blaze counter on it. For as long as that land has a blaze counter on it, it has "At the beginning of your upkeep, this land deals 1 damage to you." (The land continues to burn after this creature has left the battlefield.)