Darksteel Reactor is a rare Artifact card from Edge of Eternities Commander (EOC), collector number 134. Current market price: $0.32, TCGplayer market prices via Scryfall.
Indestructible (Effects that say "destroy" don't destroy this artifact.) At the beginning of your upkeep, you may put a charge counter on this artifact. When this artifact has twenty or more charge counters on it, you win the game.