Day of the Dragons is a rare Enchantment card from Commander 2015 (C15), collector number 91. Current market price: $0.19, TCGplayer market prices via Scryfall.
When this enchantment enters, exile all creatures you control. Then create that many 5/5 red Dragon creature tokens with flying. When this enchantment leaves the battlefield, sacrifice all Dragons you control. Then return the exiled cards to the battlefield under your control.