Chromium is a rare Legendary Creature — Elder Dragon card from Chronicles (CHR), collector number 74. Current market price: $3.48, TCGplayer market prices via Scryfall.
Flying Rampage 2 (Whenever this creature becomes blocked, it gets +2/+2 until end of turn for each creature blocking it beyond the first.) At the beginning of your upkeep, sacrifice Chromium unless you pay {W}{U}{B}.