World at War is a rare Sorcery card from Rise of the Eldrazi (ROE), collector number 172. Current market price: $12.63 (foil $19.82), TCGplayer market prices via Scryfall.
After the second main phase this turn, there's an additional combat phase followed by an additional main phase. At the beginning of that combat, untap all creatures that attacked this turn. Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)